My first graphics card....well my second

A bit more poking around this evening has now got it accessing on-chip RAM. It's pretty simple (and ropey) but it works. Shown is a screen dump from a BBC Micro loaded into memory as a .HEX file and a bit of colour at the bottom. Next up, I'll be going through some of the BBC Micro implementations on the net and pick out my favourite (looking like Mike Stirling's at present) to hack together a full BBC / HDMI on a DE0.

One thing I've discovered in the past few days is that most computer monitors (as opposed to TV's) won't support the normal SD modes i.e. 576i, which is what I was hoping for, as that would allow me to use the original 6845 timings to drive the DVI/HDMI. Looks like that's out though as my monitor requires a line rate of at least 30kHz and a frame rate of over 50Hz. The first obstacle can be avoided by buffering a line of video output at 15625Hz and outputting it twice. The second is a bit more tricky. I'm either going to have to buffer the entire frame and output at 60Hz (yuck - this will lead to gittery looking games) or maybe just cheat by running the BBC's master clock at 33Mhz instead of 32!

This is now my second attempt at a graphics card. The first one was a real hardware project, not just fpga but was a little less powerful at 32x48 pixels!