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The I/O ports for this clock are shown in Tbls.~\ref{tbl:iowishbone}

\begin{table}[htbp]

\begin{center}

\begin{portlist}

i\_clk & 1 & Input & System clock, used for time and wishbone interfaces.\\\hline

i\_wb\_cyc & 1 & Input & Wishbone bus cycle wire.\\\hline

i\_wb\_stb & 1 & Input & Wishbone strobe.\\\hline

i\_wb\_we & 1 & Input & Wishbone write enable.\\\hline

i\_wb\_addr & 5 & Input & Wishbone address.\\\hline

i\_wb\_data & 32 & Input & Wishbone bus data register for use when writing

        (configuring) the core from the bus.\\\hline

o\_wb\_ack & 1 & Output & Return value acknowledging a wishbone write, or

                signifying valid data in the case of a wishbone read request.

                \\\hline

o\_wb\_stall & 1 & Output & Indicates the device is not yet ready for another

                wishbone access, effectively stalling the bus.\\\hline

o\_wb\_data & 32 & Output & Wishbone data bus, returning data values read

                from the interface.\\\hline

\end{portlist}

\caption{Wishbone I/O Ports}\label{tbl:iowishbone}

\end{center}\end{table}

and~Tbl.~\ref{tbl:ioother}.

\begin{table}[htbp]

\begin{center}

\begin{portlist}

o\_sseg & 32 & Output & Lines to control a seven segment display, to be

                sent to that display's driver.  Each eight bit byte controls

                one digit in the display, with the bottom bit in the byte

                controlling the decimal point.\\\hline

o\_led & 16 & Output & Output LED's, consisting of a 16--bit counter counting

                from zero to all ones each minute, and synchronized with each

                minute so as to create an indicator of when the next minute

                will take place when only the hours and minutes can be

                displayed.\\\hline

o\_interrupt & 1 & Output & A pulsed/strobed interrupt line.  When the

                clock needs to generate an interrupt, it will set this line

                high for one clock cycle.  \\\hline

o\_ppd & 1 & Output & A `pulse per day' signal which can be fed into the

        real--time date module.  This line will be high on the clock before

        the stroke of midnight, allowing the date module to turn over to the

        next day at exactly the same time the clock module turns over to the

        next day.\\\hline

i\_hack & 1 & Input & When this line is raised, copies are made of the

        internal state registers on the next clock.  These registers can then

        be used for an accurate time hack regarding the state of the clock

        at the time this line was strobed.\\\hline

\end{portlist}

\caption{Other I/O Ports}\label{tbl:ioother}

\end{center}\end{table}

Tbl.~\ref{tbl:iowishbone} reiterates the wishbone I/O values just discussed in

Chapt.~\ref{chap:wishbone}, and so need no further discussion here.