I modified the test project of the Master Slave SPI Core for a Nexys3 board but I don't understand how the LEDs and buttons work because I am not getting any correlation between the LEDs lighted up and what I capture on my MOSI and MISO lines..

Hello Salman,

If you ported the 'spi_master_atlys_top.vhd' project, you should have a visual correlation of the LEDs and the sliding switches. On the Atlys, each LED is in front of the sliding switches, and they are arranged as the 8 bits of a word.

The 'spi_master_atlys_top.vhd' circuit instantiates the master and slave cores, and wires them internally as a physical loopback, exposing the api pins for probing by a LA, together with the cores flow control flags.

The buttons select which received word is shown on the LEDs. btLEFT and btDOWN will load the first word, which is the switches, so you can visually compare the received bits and the switches.

However, I do not know whether the NEXYS has the same mapping for the LEDs, switches and buttons. But you should be able to route them via the UCF file.

- Jonny