M4-GA-ROM-BC v1 Update

 Computer Room
Nov 112013
 

I’ve received my M4-GA-ROM-BC v1 PCBs from OSH Park and assembled them. They work, with the following errata:

  1. 10k pull-up resistor must be added between pins 20 and 24 of the ROM chip.
  2. 10k pull-up resistor must be added between pins 20 and 27 of the EPROM chip.
  3. The finished board is just a little bit too tall to fit under the aluminum shield on US Model 4 computers.

I will probably create a new version of this PCB to address those issues. I’ll add places for the two pull-up resistors, which keep the chip enable pin of the non-jumper-selected chip from floating, and I’ll look into using some different Mill-Max socket contacts to reduce the assembled height of the board. I’ll also switch to a right-angle header for the ROM/EPROM selection jumper.

I’m also still struggling a bit to get the new auto-boot feature of the FreHD working on my computer, but I’ll probably get over that hurdle soon.