EB6502 VGA V3

EB6502 VGA V3

Working on the V3 of my hobby computer video module.

My first module was text mode only SVGA (800x600x2)

V2 was 400x300x16.  I was never able to make the V2 stable enough to use.

I've moved on to 320x240x16.  My goal for the project is to create a Loderunner appliance.

I've been working with an Australian friend who has ported the game to other platforms.

His guidance has been crucial to my success thus far.

The AppleII version of Loderunner requires 280x192.   As such, I' doing 320x240.

Lots of great lessons in porting an AppleII game to the hardware - I think the knowledge will come in handy for porting future games. Once I'm done with Lodrunner, time and energy permitting, maybe I'll give UltimaIV a try.

Anyway, the 320x240 has gone through a few iterations.  This is the design that I've settled on (for now).   My process was to put the device together on breadboard, fiddle around until it works, and then write up the schematic.   The next step (this step) was to build another version of the module on breadboards using the schematic.  I'm doing this to verify that the schematic is correct before I order PCBs.

This blog post documents the process of rebuilding the V3 VGA according to the schematic.

Here is the schematic - still working on getting this back up on github

Here Is the 25.175MHz clock and chips laid out on the breadboards with power rails.

Adding power

 

Running clock signals and counters into the horizontal and vertical timing

Hooking up the pixel counters

Wiring up the address bus

Connecting the address bus to the memory

Wiring up the data bus, the multiplexer and pixel register.

Time to solder up some ribbon connectors

Putting them on the board to solder in the pins keeps the pin headers straight

Finished adapter

Connectors on the board, starting to wire up the signals

Wiring up video select, the video output, video write signals

All done and hooked up to the computer

Here is the old module and the new module side by side

Here's the module running a test program on a VGA monitor

OK, thats it for now.  

 Next step will be to give the schematics another good look and then send them off to JLCPCB.

I previously created a V1 PCB for my build which has been amazing.   The PCB includes CPU, RAM, ROM, 2 VIAs, an ACIA and expansion ports.   It's been super reliable, but I need to rev the PCB in order to reach my goal.  I'm having to adjust the hardware to meet the demands of the ported game.  I'm needing to have 48KB contiguous memory which is forcing me to upgrade my RAM and move my memory map around.  

I built an emulator to test / debug and port the game.   Once the PCBs arrive, it will be time to get the game running on the real hardware.   Still much to do.