You are right Neil, I had 28C256 EEPROMs capability on a prototype but later dropped it thinking nobody would need that much for a “monitor” capacity hoping to reduce jumper options - I never learn!
On the V2 boards it’s not too much of a hack to splice in a 28C256 for a 28C64.
On the 28C256 pin 1 needs to go to P39 pin 7 (the 1k pull-up is probably OK). This is the new PROM A14
JP9 pin 1 needs to go to U3 pin 6. This is the new PROM A13.
P39 is jumpered 5-6 for the PROM A12.
That’s it. Remember this is for EEPROMs 28C256’s the UV EPROM 27C256’s are different.
John
From: David Fry [mailto:dgf...@googlemail.com]
Sent: Saturday, March 22, 2014 12:12 AM
To: n8vem...@googlegroups.com
Cc: mon...@vitasoft.org
Subject: Re: [N8VEM-S100:2842] Re: BASIC in ROM - Any Interest?
I thought the Z80 V2 board flipped between 4k pages,
if it could do 8k pages then there would be enough ROM capacity in a 28C256 for both the Z80 monitor and the Nascom Basic Neil is working on.
David Fry
On Saturday, March 22, 2014 1:54:35 AM UTC, monahanz wrote:
FWIW, that’s actually one of the “improvements” on the V2 version of that board.
http://s100computers.com/My%20System%20Pages/Z80%20Board/Z80%20CPU%20Board.htm#V2 Z80 CPU Board
John
From: n8ve...@googlegroups.com [mailto:n8ve...@googlegroups.com] On Behalf Of David Fry
Sent: Friday, March 21, 2014 3:59 PM
To: n8ve...@googlegroups.com
Subject: Re: [N8VEM-S100:2842] Re: BASIC in ROM - Any Interest?
Just throwing an idea out there,
how about modifying the Z80 board to permit ROM page flipping between two 8k pages of a 28C256 (pin 1 - A14 of the 28C256 would be pulled high so only the top half of the 28C256 would be used) to permit the possibilty of jumping to Basic from a Z80 monitor menu option. When you're finished you hit reset and you're back at the Z80 monitor then you can boot into CP/M or what ever. The Z80 monitor would need to be updated to remove it's current page flip operation but I think that might make a great all in one solution.
On Friday, March 21, 2014 8:01:44 PM UTC, nbreeden wrote:
Update for 3/21
I've uploaded information on the modification I made to the V1 Z-80 CPU Card to allow a full 8K EPROM to be addressed, look in the 'Builder Journals' area under 'Neil B'.
BASIC Interpreter update:
2 minor bugs have been fixed.
The input and crunch buffer lengths have been increased from 80 to 160 bytes.
I picked 160 as increasing the buffer size takes away free memory for the BASIC program to reside in.
I've moved the hardware specific portions (the I/O interfaces) into separate files to make adding new interfaces easier..
The build environment has been updated to support multiple I/O modules.
Support for the following I/O sub-systems has been coded:
N8VEM Serial I/O USB Adapter - Tested
N8VEM Setial I/O SCC1 - Untested
N8VEM Setial I/O SCC2 - Untested
N8VEM Utility Board UART (16550) - Tested - This provides a model for 16550/16450/8250 UARTs
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