Date   : Sat, 28 Aug 1982 17:07:00-EDT
From   : Keith Petersen <W8SDZ@Mit-Mc>
Subject: Godbout Z80 modifications

The following is relayed from my RCPM system.  Replies to author,
please, not me.  Thanks.

---

S. Kluger              El Paso RCPM (915) 598-1668 

El Paso, TX, 08-27-82

The following is a modification to the GODBOUT Z-80 CPU board to enhance
it's reliability and is applicable for all boards REV J or earlier. I was
given this mod by CompuPro today, did the changes and it works great.....

The Z-80 CPU may have a problem addressing the on-board sockets if they
hold HM6116-compatible RAMs. The problem I encountered and fixed with this
mod was the following:

I am using an old Hayes 80-103A modem card with a hardware modification 
to decode the lower 8 address bits. The port is 90H. When addressing the
board using Z-80 I/O instructions (LXI B,9090H, COUT A), everything worked
fine. Using 8080 I/O, it did the following: It deposited (read closely)
the RAM page number (F8 or above) at PAGE+PORT. Example: at F890H it wrote
a F8, at F990H it wrote a F9, at FA90H it wrote a FA, and so on. It did that
only on RAM chips plugged into the CPU board socket.

This is what you'll have to do to make your board work:
1. Connect a jumper wire from U15 pin 1 to U14 pin 1. U14-1 may be connected
   to Vcc. If so, remove the short to Vcc.
2. Connect a jumper wire from U14 pin 2 to "A" of J2.
3. Break trace going TO "A" of J2.

Please note that "A" of J2 is wrong in the schematic but right on the board.
In the schematic, "A" is "B" and "B" is "A". 

This mod removes "pwr" as write strobe for the 6116 and replaces it
with "mwrite".

I was also told that REV J and earlier boards MAY not work right when converted
to 6MHz operation.