Accessing all 41 pins on the BX


#1

Short Version
How easy/hard is it to turn all 41 pins of the BX into GPIO? Will I have to remove the LED? Some of the pins are shared by the USB programmer right? BTW, I already own the DIP breakout board from Tall Dog.

Back Story
In 2018, I designed a 65C02 based SBC. This year, I’d like to finally put a video chip in it. Of course, my BX FPGA is the chip of choice. :smiley:

Now, I’m thinking about removing my old glue logic and do everything in the FPGA. The video and glue.
In the planning stages, I believe I can get 64 colors and complete memory control. However, this is going to take exactly 41 pins. Which is what the BX has. My scheme is to use character based graphics and external RAM (shared with the 65C02).

Pinouts

  • Address 16
  • Data 8
  • 02 1
  • /RESET 1
  • R/W 1
  • /RD 1
  • /WR 1
  • /RAM 1
  • /ROM 1
  • /IO 1
  • VGA_CLK 1
  • VGA_OUT 6
  • VGA_HSYNC 1
  • VGA_VSYNC 1

I could pull some of the address lines off if needed. I want to have a full 64KiB (vs. 16KiB it has now) and having a very fine-grained address decoder would be great.

Thanks for any input!

EDIT

Crap. I think I will have to pull some lines off the address bus anyway. I forgot that I want to trigger an interrupt from the video chip…anyway, not relevant to the topic at hand.