Playing with VHDL

On my old website there are two projects using VHDL on a Spartan-3e FPGA.  Recently, I decided to get back to playing with that again.  The project goal this time was to produce a VGA output - in FPGA circles, this is by now the equivalent of a "Hello, World!" program.  Nothing new, but I felt it was important to do from scratch without copying any bits so I see how the whole thing fits together.

The Spartan 3e "S3E Sample Pack" board, a freebie I picked up a few years back.

The picture shows the board and the VGA connector: with only 4 I/O pins on one connector, I made it a monochrome (green) only interface.  The pins used are horizontal sync, vertical sync, and 2 bits of video signal.  With a bit of soldering I could make it monochrome grey, or I could add another connector to get more output lines to get real color.  For playing with synchronization, the quick and dirty adapter giving 4 intensities of green (well, 3 green plus black) is quite sufficient.  (...more...)