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malikpearl |
------------------------------------------------------------------------
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-- uartcomponent.vhd
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------------------------------------------------------------------------
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-- Author: Dan Pederson
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-- Copyright 2004 Digilent, Inc.
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------------------------------------------------------------------------
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-- Description: This file defines a UART which transfers data to and
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-- from serial and parallel information. It requires two
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-- major processes: receiving and transferring. The
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-- receiving portion reads serially transmitted data, and
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-- converts it into parallel data, while the transferring
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-- portion reads parallel data, and transmits it as serial
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-- data. There are three error signals provided with this
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-- UART. They are frame error, parity error, and overwrite
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-- error signals. This UART is configured to use an ODD
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-- parity bit at a baud rate of 9600.
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--
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------------------------------------------------------------------------
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-- Revision History:
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-- 07/15/04 (DanP) Created
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-- 05/24/05 (DanP) Updated commenting style
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-- 06/06/05 (DanP) Synchronized state machines to fix timing bug
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------------------------------------------------------------------------
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library IEEE;
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use IEEE.STD_LOGIC_1164.ALL;
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use IEEE.STD_LOGIC_ARITH.ALL;
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use IEEE.STD_LOGIC_UNSIGNED.ALL;
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-------------------------------------------------------------------------
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--
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--Title: UARTcomponent entity
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--
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--Inputs: 7 : RXD
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-- CLK
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-- DBIN
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-- RDA
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-- RD
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-- WR
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-- RST
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--
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--Outputs: 7 : TXD
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-- DBOUT
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-- RDA
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-- TBE
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-- PE
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-- FE
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-- OE
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--
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--Description: This describes the UART component entity. The inputs are
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-- the Pegasus 50 MHz clock, a reset button, The RXD from
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-- the serial cable, an 8-bit data bus from the parallel
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-- port, and Read Data Available (RDA)and Transfer Buffer
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-- Empty(TBE) handshaking signals. The outputs are the TXD
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-- signal for the serial port, an 8-bit data bus for the
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-- parallel port, RDA and TBE handshaking signals, and three
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-- error signals for parity, frame, and overwrite errors.
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--
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-------------------------------------------------------------------------
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entity UARTcomponent is
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Port ( TXD : out std_logic := '1'; -- Transmitted serial data output
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RXD : in std_logic; -- Received serial data input
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CLK : in std_logic; -- Clock signal
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DBIN : in std_logic_vector (7 downto 0); -- Input parallel data to be transmitted
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DBOUT : out std_logic_vector (7 downto 0); -- Recevived parallel data output
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RDA : inout std_logic; -- Read Data Available
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TBE : out std_logic := '1'; -- Transfer Buffer Emty
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RD : in std_logic;
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WR : in std_logic;
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PE : out std_logic; -- Parity error
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FE : out std_logic; -- Frame error
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OE : out std_logic; -- Overwrite error
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RST : in std_logic := '0'); -- Reset signal
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end UARTcomponent;
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architecture Behavioral of UARTcomponent is
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------------------------------------------------------------------------
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-- Local Type and Signal Declarations
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------------------------------------------------------------------------
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-------------------------------------------------------------------------
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--Title: Local Type Declarations
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--
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--Description: There are two state machines used in this entity. The
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-- rstate is used to synchronize the receiving portion of
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-- the UART, and the tstate is used to synchronize the
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-- sending portion of the UART.
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--
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-------------------------------------------------------------------------
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type rstate is (
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strIdle,
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strEightDelay,
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strGetData,
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strWaitFor0,
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strWaitFor1,
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strCheckStop
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);
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type tstate is (
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sttIdle,
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sttTransfer,
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sttShift,
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sttDelay,
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sttWaitWrite
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);
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-------------------------------------------------------------------------
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--
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--Title: Local Signal Declarations
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--
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--Description: The constants and signals used by this entity are
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-- described below:
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--
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-- -baudRate : This is the Baud Rate constant used to
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-- synchronize the Pegasus 50 MHz clock with a
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-- baud rate of 9600. To get this number, divide
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-- 50MHz by 9600.
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-- -baudDivide : This is the Baud Rate divider used to safely
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-- read data transmitted at a baud rate of 9600.
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-- It is simply the above described baudRate
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-- constant divided by 16.
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--
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-- -rdReg : this is the receive holding register
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-- -rdSReg : this is the receive shift register
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-- -tfReg : this is the transfer holding register
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-- -tfSReg : this is the transfer shifting register
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-- -clkDiv : counter used to get rClk
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-- -ctr : used for delay times
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-- -tfCtr : used to delay in the transfer process
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-- -dataCtr : counts the number of read data bits
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-- -parError : parity error bit
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-- -frameError : frame error bit
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-- -CE : clock enable bit for the writing latch
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-- -ctRst : reset for the ctr
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-- -load : load signal used to load the transfer shift
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-- register
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-- -shift : shift signal used to unload the transfer
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-- shift register
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-- -par : represents the parity in the transfer
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-- holding register
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-- -tClkRST : reset for the tfCtr
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-- -rShift : shift signal used to load the receive shift
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-- register
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-- -dataRST : reset for the dataCtr
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-- -dataIncr : signal to increment the dataCtr
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-- -tfIncr : signal to increment the tfCtr
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-- -tDelayCtr : counter used to delay the transfer state
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-- machine.
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-- -tDelayRst : reset signal for the tDelayCtr counter.
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--
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-- The following signals are used by the two state machines
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-- for state control:
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-- -Receive State Machine : strCur, strNext
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-- -Transfer State Machine : sttCur, sttNext
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--
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-------------------------------------------------------------------------
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-- constant baudRate : std_logic_vector(12 downto 0) := "1 0100 0101 1000";
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-- constant baudRate : std_logic_vector(12 downto 0) := conv_std_logic_vector(1406,13); --19200
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constant baudRate : std_logic_vector(12 downto 0) := conv_std_logic_vector(234,13); -- 115 200
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-- constant baudRate : std_logic_vector(12 downto 0) := conv_std_logic_vector(482,13); -- 56 000
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-- baudrate is set for 115 200 at 27MHz clock freq
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constant baudDivide : std_logic_vector(8 downto 0) := conv_std_logic_vector(15,9);
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signal rdReg : std_logic_vector(7 downto 0) := "00000000";
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signal rdSReg : std_logic_vector(9 downto 0) := "1111111111";
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signal tfReg : std_logic_vector(7 downto 0);
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signal tfSReg : std_logic_vector(10 downto 0) := "11111111111";
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signal clkDiv : std_logic_vector(9 downto 0) := "0000000000";
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signal ctr : std_logic_vector(3 downto 0) := "0000";
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signal tfCtr : std_logic_vector(3 downto 0) := "0000";
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signal dataCtr : std_logic_vector(3 downto 0) := "0000";
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signal parError : std_logic;
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signal frameError : std_logic;
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signal CE : std_logic;
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signal ctRst : std_logic := '0';
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signal load : std_logic := '0';
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signal shift : std_logic := '0';
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signal par : std_logic;
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signal tClkRST : std_logic := '0';
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signal rShift : std_logic := '0';
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signal dataRST : std_logic := '0';
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signal dataIncr : std_logic := '0';
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signal tfIncr : std_logic := '0';
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signal tDelayCtr : std_logic_vector (12 downto 0);
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signal tDelayRst : std_logic := '0';
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signal strCur : rstate := strIdle;
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signal strNext : rstate;
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signal sttCur : tstate := sttIdle;
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signal sttNext : tstate;
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-------------------------------------------------------------------------
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-- Module Implementation
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-------------------------------------------------------------------------
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begin
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-------------------------------------------------------------------------
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--
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--Title: Initial signal definitions
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--
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--Description: The following lines of code define 4 internal and 1
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-- external signal. The most significant bit of the rdSReg
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-- signifies the frame error bit, so frameError is tied to
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-- that signal. The parError is high if there is a parity
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-- error, so it is set equal to the inverse of rdSReg(8)
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-- XOR-ed with the data bits. In this manner, it can
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-- determine if the parity bit found in rdSReg(8) matches
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-- the data bits. The parallel information output is equal
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-- to rdReg, so DBOUT is set equal to rdReg. Likewise, the
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-- input parallel information is equal to DBIN, so tfReg is
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-- set equal to DBIN. Because the tfSReg is used to shift
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-- out transmitted data, the TXD port is set equal to the
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-- first bit of tfsReg. Finally, the par signal represents
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-- the parity of the data, so par is set to the inverse of
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-- the data bits XOR-ed together. This UART can be changed
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-- to use EVEN parity if the "not" is omitted from the par
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-- definition.
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--
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-------------------------------------------------------------------------
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frameError <= not rdSReg(9);
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parError <= not ( rdSReg(8) xor (((rdSReg(0) xor rdSReg(1)) xor
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(rdSReg(2) xor rdSReg(3))) xor ((rdSReg(4) xor rdSReg(5)) xor
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(rdSReg(6) xor rdSReg(7)))) );
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DBOUT <= rdReg;
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tfReg <= DBIN;
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TXD <= tfsReg(0);
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par <= not ( ((tfReg(0) xor tfReg(1)) xor (tfReg(2) xor tfReg(3))) xor
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((tfReg(4) xor tfReg(5)) xor (tfReg(6) xor tfReg(7))) );
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-------------------------------------------------------------------------
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--
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--Title: Clock Divide counter
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--
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--Description: This process defines clkDiv as a signal that increments
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-- with the clock up until it is either reset by ctRst, or
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-- equals baudDivide. This signal is used to define a
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-- counter called ctr that increments at the rate of the
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-- divided baud rate.
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--
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-------------------------------------------------------------------------
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process (CLK, clkDiv)
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begin
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if (CLK = '1' and CLK'event) then
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if (clkDiv = baudDivide or ctRst = '1') then
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clkDiv <= "0000000000";
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else
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clkDiv <= clkDiv +1;
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end if;
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end if;
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end process;
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-------------------------------------------------------------------------
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--
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--Title: Transfer delay counter
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--
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--Description: This process defines tDelayCtr as a counter that runs
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-- until it equals baudRate, or until it is reset by
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-- tDelayRst. This counter is used to measure delay times
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-- when sending data out on the TXD signal. When the
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-- counter is equal to baudRate, or is reset, it is set
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-- equal to 0.
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--
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-------------------------------------------------------------------------
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process (CLK, tDelayCtr)
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begin
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if (CLK = '1' and CLK'event) then
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if (tDelayCtr = baudRate or tDelayRst = '1') then
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tDelayCtr <= "0000000000000";
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else
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tDelayCtr <= tDelayCtr+1;
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end if;
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end if;
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end process;
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-------------------------------------------------------------------------
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--
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--Title: ctr set up
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--
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--Description: This process sets up ctr, which uses clkDiv to count
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-- increase at a rate needed to properly receive data in
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-- from RXD. If ctRst is strobed, the counter is reset. If
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-- clkDiv is equal to baudDivide, then ctr is incremented
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-- once. This signal is used by the receiving state machine
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-- to measure delay times between RXD reads.
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--
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-------------------------------------------------------------------------
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process (CLK)
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begin
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if CLK = '1' and CLK'Event then
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if ctRst = '1' then
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ctr <= "0000";
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elsif clkDiv = baudDivide then
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ctr <= ctr + 1;
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else
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ctr <= ctr;
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end if;
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end if;
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end process;
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-------------------------------------------------------------------------
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--
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--Title: transfer counter
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--
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--Description: This process makes tfCtr increment whenever the tfIncr
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-- signal is strobed high. If the tClkRst signal is strobed
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-- high, the tfCtr is reset to "0000." This counter is used
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-- to keep track of how many data bits have been
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-- transmitted.
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--
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-------------------------------------------------------------------------
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process (CLK, tClkRST)
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begin
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if (CLK = '1' and CLK'event) then
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if tClkRST = '1' then
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tfCtr <= "0000";
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elsif tfIncr = '1' then
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tfCtr <= tfCtr +1;
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end if;
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end if;
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end process;
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-------------------------------------------------------------------------
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--
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--Title: Error and RDA flag controller
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--
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--Description: This process controls the error flags FE, OE, and PE, as
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-- well as the Read Data Available (RDA) flag. When CE goes
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-- high, it means that data has been read into the rdSReg.
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-- This process then analyzes the read data for errors, sets
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-- rdReg equal to the eight data bits in rdSReg, and flags
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-- RDA to indicate that new data is present in rdReg. FE
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-- and PE are simply equal to the frameError and parError
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-- signals. OE is flagged high if RDA is already high when
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-- CE is strobed. This means that unread data was still in
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-- the rdReg when it was written over with the new data.
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--
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-------------------------------------------------------------------------
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process (CLK, RST, RD, CE)
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begin
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if RD = '1' or RST = '1' then
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FE <= '0';
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OE <= '0';
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RDA <= '0';
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PE <= '0';
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elsif CLK = '1' and CLK'event then
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if CE = '1' then
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FE <= frameError;
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PE <= parError;
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rdReg(7 downto 0) <= rdSReg (7 downto 0);
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347 |
|
|
if RDA = '1' then
|
348 |
|
|
OE <= '1';
|
349 |
|
|
else
|
350 |
|
|
OE <= '0';
|
351 |
|
|
RDA <= '1';
|
352 |
|
|
end if;
|
353 |
|
|
end if;
|
354 |
|
|
end if;
|
355 |
|
|
end process;
|
356 |
|
|
-------------------------------------------------------------------------
|
357 |
|
|
--
|
358 |
|
|
--Title: Receiving shift register
|
359 |
|
|
--
|
360 |
|
|
--Description: This process controls the receiving shift register
|
361 |
|
|
-- (rdSReg). Whenever rShift is high, implying that data
|
362 |
|
|
-- needs to be shifted in, rdSReg is shifts in RXD to the
|
363 |
|
|
-- most significant bit, while shifting its existing data
|
364 |
|
|
-- right.
|
365 |
|
|
--
|
366 |
|
|
-------------------------------------------------------------------------
|
367 |
|
|
process (CLK, rShift)
|
368 |
|
|
begin
|
369 |
|
|
if CLK = '1' and CLK'Event then
|
370 |
|
|
if rShift = '1' then
|
371 |
|
|
rdSReg <= (RXD & rdSReg(9 downto 1));
|
372 |
|
|
end if;
|
373 |
|
|
end if;
|
374 |
|
|
end process;
|
375 |
|
|
-------------------------------------------------------------------------
|
376 |
|
|
--
|
377 |
|
|
--Title: Incoming Data counter
|
378 |
|
|
--
|
379 |
|
|
--Description: This process controls the dataCtr to keep track of
|
380 |
|
|
-- shifted values into the rdSReg. The dataCtr signal is
|
381 |
|
|
-- incremented once every time dataIncr is strobed high.
|
382 |
|
|
--
|
383 |
|
|
-------------------------------------------------------------------------
|
384 |
|
|
|
385 |
|
|
process (CLK, dataRST)
|
386 |
|
|
begin
|
387 |
|
|
if (CLK = '1' and CLK'event) then
|
388 |
|
|
if dataRST = '1' then
|
389 |
|
|
dataCtr <= "0000";
|
390 |
|
|
elsif dataIncr = '1' then
|
391 |
|
|
dataCtr <= dataCtr +1;
|
392 |
|
|
end if;
|
393 |
|
|
end if;
|
394 |
|
|
end process;
|
395 |
|
|
-------------------------------------------------------------------------
|
396 |
|
|
--
|
397 |
|
|
--Title: Receiving State Machine controller
|
398 |
|
|
--
|
399 |
|
|
--Description: This process takes care of the Receiving state machine
|
400 |
|
|
-- movement. It causes the next state to be evaluated on
|
401 |
|
|
-- each rising edge of CLK. If the RST signal is strobed,
|
402 |
|
|
-- the state is changed to the default starting state,
|
403 |
|
|
-- which is strIdle
|
404 |
|
|
--
|
405 |
|
|
-------------------------------------------------------------------------
|
406 |
|
|
process (CLK, RST)
|
407 |
|
|
begin
|
408 |
|
|
if CLK = '1' and CLK'Event then
|
409 |
|
|
if RST = '1' then
|
410 |
|
|
strCur <= strIdle;
|
411 |
|
|
else
|
412 |
|
|
strCur <= strNext;
|
413 |
|
|
end if;
|
414 |
|
|
end if;
|
415 |
|
|
end process;
|
416 |
|
|
-------------------------------------------------------------------------
|
417 |
|
|
--
|
418 |
|
|
--Title: Receiving State Machine
|
419 |
|
|
--
|
420 |
|
|
--Description: This process contains all of the next state logic for the
|
421 |
|
|
-- Receiving state machine.
|
422 |
|
|
--
|
423 |
|
|
-------------------------------------------------------------------------
|
424 |
|
|
process (strCur, ctr, RXD, dataCtr)
|
425 |
|
|
begin
|
426 |
|
|
case strCur is
|
427 |
|
|
-------------------------------------------------------------------------
|
428 |
|
|
--
|
429 |
|
|
--Title: strIdle state
|
430 |
|
|
--
|
431 |
|
|
--Description: This state is the idle and startup default stage for the
|
432 |
|
|
-- Receiving state machine. The machine stays in this state
|
433 |
|
|
-- until the RXD signal goes low. When this occurs, the
|
434 |
|
|
-- ctRst signal is strobed to reset ctr for the next state,
|
435 |
|
|
-- which is strEightDelay.
|
436 |
|
|
--
|
437 |
|
|
-------------------------------------------------------------------------
|
438 |
|
|
when strIdle =>
|
439 |
|
|
dataIncr <= '0';
|
440 |
|
|
rShift <= '0';
|
441 |
|
|
dataRst <= '1';
|
442 |
|
|
CE <= '0';
|
443 |
|
|
ctRst <= '1';
|
444 |
|
|
|
445 |
|
|
if RXD = '0' then
|
446 |
|
|
strNext <= strEightDelay;
|
447 |
|
|
else
|
448 |
|
|
strNext <= strIdle;
|
449 |
|
|
end if;
|
450 |
|
|
-------------------------------------------------------------------------
|
451 |
|
|
--
|
452 |
|
|
--Title: strEightDelay state
|
453 |
|
|
--
|
454 |
|
|
--Description: This state simply delays the state machine for eight clock
|
455 |
|
|
-- cycles. This is needed so that the incoming RXD data
|
456 |
|
|
-- signal is read in the middle of each data emission. This
|
457 |
|
|
-- ensures an accurate RXD signal reading. ctr counts from
|
458 |
|
|
-- 0 to 8 to keep track of rClk cycles. When it equals 8
|
459 |
|
|
-- (1000) the next state, strWaitFor0, is loaded. During
|
460 |
|
|
-- this state, the dataRst signal is strobed high to reset
|
461 |
|
|
-- the shift-in data counter (dataCtr).
|
462 |
|
|
--
|
463 |
|
|
-------------------------------------------------------------------------
|
464 |
|
|
when strEightDelay =>
|
465 |
|
|
dataIncr <= '0';
|
466 |
|
|
rShift <= '0';
|
467 |
|
|
dataRst <= '1';
|
468 |
|
|
CE <= '0';
|
469 |
|
|
ctRst <= '0';
|
470 |
|
|
|
471 |
|
|
if ctr(3 downto 0) = "1000" then
|
472 |
|
|
strNext <= strWaitFor0;
|
473 |
|
|
else
|
474 |
|
|
strNext <= strEightDelay;
|
475 |
|
|
end if;
|
476 |
|
|
-------------------------------------------------------------------------
|
477 |
|
|
--
|
478 |
|
|
--Title: strGetData state
|
479 |
|
|
--
|
480 |
|
|
--Description: In this state, the dataIncr and rShift signals are
|
481 |
|
|
-- strobed high for one clock cycle. By doing this, the
|
482 |
|
|
-- rdSReg shift register shifts in RXD once, while the
|
483 |
|
|
-- dataCtr is incremented by one. This state simply
|
484 |
|
|
-- captures the incoming data on RXD into the rdSReg shift
|
485 |
|
|
-- register. The next state loaded is strWaitFor0, which
|
486 |
|
|
-- starts the two delay states needed between data shifts.
|
487 |
|
|
--
|
488 |
|
|
-------------------------------------------------------------------------
|
489 |
|
|
when strGetData =>
|
490 |
|
|
CE <= '0';
|
491 |
|
|
dataRst <= '0';
|
492 |
|
|
ctRst <= '0';
|
493 |
|
|
dataIncr <= '1';
|
494 |
|
|
rShift <= '1';
|
495 |
|
|
|
496 |
|
|
strNext <= strWaitFor0;
|
497 |
|
|
-------------------------------------------------------------------------
|
498 |
|
|
--
|
499 |
|
|
--Title: strWaitFor0 state
|
500 |
|
|
--
|
501 |
|
|
--Description: This state is a delay state, which delays the receive
|
502 |
|
|
-- state machine if not all of the incoming serial data has
|
503 |
|
|
-- not been shifted in yet. If dataCtr does not equal 10
|
504 |
|
|
-- (1010), the state is stayed in until the fourth bit of
|
505 |
|
|
-- ctr is equal to 1. When this happens, half of the delay
|
506 |
|
|
-- has been achieved, and the second delay state is loaded,
|
507 |
|
|
-- which is strWaitFor1. If dataCtr does equal 10 (1010),
|
508 |
|
|
-- all of the needed data has been acquired, so the
|
509 |
|
|
-- strCheckStop state is loaded to check for errors and
|
510 |
|
|
-- reset the receive state machine.
|
511 |
|
|
--
|
512 |
|
|
-------------------------------------------------------------------------
|
513 |
|
|
when strWaitFor0 =>
|
514 |
|
|
CE <= '0';
|
515 |
|
|
dataRst <= '0';
|
516 |
|
|
ctRst <= '0';
|
517 |
|
|
dataIncr <= '0';
|
518 |
|
|
rShift <= '0';
|
519 |
|
|
|
520 |
|
|
if dataCtr = "1010" then
|
521 |
|
|
strNext <= strCheckStop;
|
522 |
|
|
elsif ctr(3) = '0' then
|
523 |
|
|
strNext <= strWaitFor1;
|
524 |
|
|
else
|
525 |
|
|
strNext <= strWaitFor0;
|
526 |
|
|
end if;
|
527 |
|
|
-------------------------------------------------------------------------
|
528 |
|
|
--
|
529 |
|
|
--Title: strEightDelay state
|
530 |
|
|
--
|
531 |
|
|
--Description: This state is much like strWaitFor0, except it waits for
|
532 |
|
|
-- the fourth bit of ctr to equal 1. Once this occurs, the
|
533 |
|
|
-- strGetData state is loaded in order to shift in the next
|
534 |
|
|
-- data bit from RXD. Because strWaitFor0 is the only state
|
535 |
|
|
-- that calls this state, no other signals need to be
|
536 |
|
|
-- checked.
|
537 |
|
|
--
|
538 |
|
|
-------------------------------------------------------------------------
|
539 |
|
|
when strWaitFor1 =>
|
540 |
|
|
CE <= '0';
|
541 |
|
|
dataRst <= '0';
|
542 |
|
|
ctRst <= '0';
|
543 |
|
|
dataIncr <= '0';
|
544 |
|
|
rShift <= '0';
|
545 |
|
|
|
546 |
|
|
if ctr(3) = '0' then
|
547 |
|
|
strNext <= strWaitFor1;
|
548 |
|
|
else
|
549 |
|
|
strNext <= strGetData;
|
550 |
|
|
end if;
|
551 |
|
|
-------------------------------------------------------------------------
|
552 |
|
|
--
|
553 |
|
|
--Title: strCheckStop state
|
554 |
|
|
--
|
555 |
|
|
--Description: This state allows the newly acquired data to be checked
|
556 |
|
|
-- for errors. The CE flag is strobed to start the
|
557 |
|
|
-- previously defined error checking process. This state is
|
558 |
|
|
-- passed straight through to the strIdle state.
|
559 |
|
|
--
|
560 |
|
|
-------------------------------------------------------------------------
|
561 |
|
|
when strCheckStop =>
|
562 |
|
|
dataIncr <= '0';
|
563 |
|
|
rShift <= '0';
|
564 |
|
|
dataRst <= '0';
|
565 |
|
|
ctRst <= '0';
|
566 |
|
|
CE <= '1';
|
567 |
|
|
strNext <= strIdle;
|
568 |
|
|
end case;
|
569 |
|
|
end process;
|
570 |
|
|
-------------------------------------------------------------------------
|
571 |
|
|
--
|
572 |
|
|
--Title: Transfer shift register controller
|
573 |
|
|
--
|
574 |
|
|
--Description: This process uses the load, shift, and clk signals to
|
575 |
|
|
-- control the transfer shift register (tfSReg). Once load
|
576 |
|
|
-- is equal to '1', the tfSReg gets a '1', the parity bit,
|
577 |
|
|
-- the data bits found in tfReg, and a '0'. Under this
|
578 |
|
|
-- format, the shift register can be used to shift out the
|
579 |
|
|
-- appropriate signal to serially transfer the data. The
|
580 |
|
|
-- data is shifted out of the tfSReg whenever shift = '1'.
|
581 |
|
|
--
|
582 |
|
|
-------------------------------------------------------------------------
|
583 |
|
|
process (load, shift, CLK, tfSReg)
|
584 |
|
|
begin
|
585 |
|
|
if CLK = '1' and CLK'Event then
|
586 |
|
|
if load = '1' then
|
587 |
|
|
tfSReg (10 downto 0) <= ('1' & par & tfReg(7 downto 0) &'0');
|
588 |
|
|
elsif shift = '1' then
|
589 |
|
|
tfSReg (10 downto 0) <= ('1' & tfSReg(10 downto 1));
|
590 |
|
|
end if;
|
591 |
|
|
end if;
|
592 |
|
|
end process;
|
593 |
|
|
-------------------------------------------------------------------------
|
594 |
|
|
--
|
595 |
|
|
--Title: Transfer State Machine controller
|
596 |
|
|
--
|
597 |
|
|
--Description: This process takes care of the Transfer state machine
|
598 |
|
|
-- movement. It causes the next state to be evaluated on
|
599 |
|
|
-- each rising edge of CLK. If the RST signal is strobed,
|
600 |
|
|
-- the state is changed to the default starting state, which
|
601 |
|
|
-- is sttIdle.
|
602 |
|
|
--
|
603 |
|
|
-------------------------------------------------------------------------
|
604 |
|
|
process (CLK, RST)
|
605 |
|
|
begin
|
606 |
|
|
if (CLK = '1' and CLK'Event) then
|
607 |
|
|
if RST = '1' then
|
608 |
|
|
sttCur <= sttIdle;
|
609 |
|
|
else
|
610 |
|
|
sttCur <= sttNext;
|
611 |
|
|
end if;
|
612 |
|
|
end if;
|
613 |
|
|
end process;
|
614 |
|
|
-------------------------------------------------------------------------
|
615 |
|
|
--
|
616 |
|
|
--Title: Transfer State Machine
|
617 |
|
|
--
|
618 |
|
|
--Description: This process controls the next state logic in the
|
619 |
|
|
-- transfer state machine. The transfer state machine
|
620 |
|
|
-- controls the shift and load signals that are used to load
|
621 |
|
|
-- and transmit the parallel data in a serial form. It also
|
622 |
|
|
-- controls the Transmit Buffer Empty (TBE) signal that
|
623 |
|
|
-- indicates if the transmit buffer (tfSReg) is in use or
|
624 |
|
|
-- not.
|
625 |
|
|
--
|
626 |
|
|
-------------------------------------------------------------------------
|
627 |
|
|
process (sttCur, tfCtr, WR, tDelayCtr)
|
628 |
|
|
begin
|
629 |
|
|
case sttCur is
|
630 |
|
|
-------------------------------------------------------------------------
|
631 |
|
|
--
|
632 |
|
|
--Title: sttIdle state
|
633 |
|
|
--
|
634 |
|
|
--Description: This state is the idle and startup default stage for the
|
635 |
|
|
-- transfer state machine. The state is stayed in until
|
636 |
|
|
-- the WR signal goes high. Once it goes high, the
|
637 |
|
|
-- sttTransfer state is loaded. The load and shift signals
|
638 |
|
|
-- are held low in the sttIdle state, while the TBE signal
|
639 |
|
|
-- is held high to indicate that the transmit buffer is not
|
640 |
|
|
-- currently in use. Once the idle state is left, the TBE
|
641 |
|
|
-- signal is held low to indicate that the transfer state
|
642 |
|
|
-- machine is using the transmit buffer.
|
643 |
|
|
--
|
644 |
|
|
-------------------------------------------------------------------------
|
645 |
|
|
when sttIdle =>
|
646 |
|
|
TBE <= '1';
|
647 |
|
|
tClkRST <= '0';
|
648 |
|
|
tfIncr <= '0';
|
649 |
|
|
shift <= '0';
|
650 |
|
|
load <= '0';
|
651 |
|
|
tDelayRst <= '1';
|
652 |
|
|
|
653 |
|
|
if WR = '0' then
|
654 |
|
|
sttNext <= sttIdle;
|
655 |
|
|
else
|
656 |
|
|
sttNext <= sttTransfer;
|
657 |
|
|
end if;
|
658 |
|
|
-------------------------------------------------------------------------
|
659 |
|
|
--
|
660 |
|
|
--Title: sttTransfer state
|
661 |
|
|
--
|
662 |
|
|
--Description: This state sets the load, tClkRST, and tDelayRst signals
|
663 |
|
|
-- high, while setting the TBE signal low. The load signal
|
664 |
|
|
-- is set high to load the transfer shift register with the
|
665 |
|
|
-- appropriate data, while the tClkRST and tDelayRst signals
|
666 |
|
|
-- are strobed to reset the tfCtr and tDelayCtr. The next
|
667 |
|
|
-- state loaded is the sttDelay state.
|
668 |
|
|
--
|
669 |
|
|
-------------------------------------------------------------------------
|
670 |
|
|
when sttTransfer =>
|
671 |
|
|
TBE <= '0';
|
672 |
|
|
shift <= '0';
|
673 |
|
|
load <= '1';
|
674 |
|
|
tClkRST <= '1';
|
675 |
|
|
tfIncr <= '0';
|
676 |
|
|
tDelayRst <= '1';
|
677 |
|
|
|
678 |
|
|
sttNext <= sttDelay;
|
679 |
|
|
-------------------------------------------------------------------------
|
680 |
|
|
--
|
681 |
|
|
--Title: sttShift state
|
682 |
|
|
--
|
683 |
|
|
--Description: This state strobes the shift and tfIncr signals high, and
|
684 |
|
|
-- checks the tfCtr to see if enough data has been
|
685 |
|
|
-- transmitted. By strobing the shift and tfIncr signals
|
686 |
|
|
-- high, the tfSReg is shifted, and the tfCtr is incremented
|
687 |
|
|
-- once. If tfCtr does not equal 9 (1001), then not all of
|
688 |
|
|
-- the bits have been transmitted, so the next state loaded
|
689 |
|
|
-- is the sttDelay state. If tfCtr does equal 9, the final
|
690 |
|
|
-- state, sttWaitWrite, is loaded.
|
691 |
|
|
--
|
692 |
|
|
-------------------------------------------------------------------------
|
693 |
|
|
when sttShift =>
|
694 |
|
|
TBE <= '0';
|
695 |
|
|
shift <= '1';
|
696 |
|
|
load <= '0';
|
697 |
|
|
tfIncr <= '1';
|
698 |
|
|
tClkRST <= '0';
|
699 |
|
|
tDelayRst <= '0';
|
700 |
|
|
|
701 |
|
|
if tfCtr = "1010" then
|
702 |
|
|
sttNext <= sttWaitWrite;
|
703 |
|
|
else
|
704 |
|
|
sttNext <= sttDelay;
|
705 |
|
|
end if;
|
706 |
|
|
-------------------------------------------------------------------------
|
707 |
|
|
--
|
708 |
|
|
--Title: sttDelay state
|
709 |
|
|
--
|
710 |
|
|
--Description: This state is responsible for delaying the transfer state
|
711 |
|
|
-- machine between transmissions. All signals are held low
|
712 |
|
|
-- while the tDelayCtr is tested. Once tDelayCtr is equal
|
713 |
|
|
-- to baudRate, the sttShift state is loaded.
|
714 |
|
|
--
|
715 |
|
|
-------------------------------------------------------------------------
|
716 |
|
|
when sttDelay =>
|
717 |
|
|
TBE <= '0';
|
718 |
|
|
shift <= '0';
|
719 |
|
|
load <= '0';
|
720 |
|
|
tClkRst <= '0';
|
721 |
|
|
tfIncr <= '0';
|
722 |
|
|
tDelayRst <= '0';
|
723 |
|
|
|
724 |
|
|
if tDelayCtr = baudRate then
|
725 |
|
|
sttNext <= sttShift;
|
726 |
|
|
else
|
727 |
|
|
sttNext <= sttDelay;
|
728 |
|
|
end if;
|
729 |
|
|
-------------------------------------------------------------------------
|
730 |
|
|
--
|
731 |
|
|
--Title: sttWaitWrite state
|
732 |
|
|
--
|
733 |
|
|
--Description: This state checks to make sure that the initial WR signal
|
734 |
|
|
-- that triggered the transfer state machine has been
|
735 |
|
|
-- brought back low. Without this state, a write signal
|
736 |
|
|
-- that is held high for a long time will result in multiple
|
737 |
|
|
-- transmissions. Once the WR signal is low, the sttIdle
|
738 |
|
|
-- state is loaded to reset the transfer state machine.
|
739 |
|
|
--
|
740 |
|
|
-------------------------------------------------------------------------
|
741 |
|
|
when sttWaitWrite =>
|
742 |
|
|
TBE <= '0';
|
743 |
|
|
shift <= '0';
|
744 |
|
|
load <= '0';
|
745 |
|
|
tClkRst <= '0';
|
746 |
|
|
tfIncr <= '0';
|
747 |
|
|
tDelayRst <= '0';
|
748 |
|
|
|
749 |
|
|
if WR = '1' then
|
750 |
|
|
sttNext <= sttWaitWrite;
|
751 |
|
|
else
|
752 |
|
|
sttNext <= sttIdle;
|
753 |
|
|
end if;
|
754 |
|
|
end case;
|
755 |
|
|
end process;
|
756 |
|
|
end Behavioral;
|