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Std EditionDual NVRAM

License: Public Domain

Published Time:2020-07-30 04:29:10
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Description

CAUTION! TESTED IN PROGRESS - UNDER CONSTRUCTION

V1.1 Board 284 Connections 33 VIAS

V1.1 Changes

- Combined 139 Config and 24 or 32 Bit Config into 1 set of jumpers
- Modified 138 Config to fix 20 Bit jumpers
- Reconfigured 139 to allow for 1M nvRAM (DS1265 / bq4016)

UPDATE: V1.0 boards have arrived

Tested with a z180 CPU card, using a AS6C4008 ram & 39SF040 ROM - Working after 20Bit Address Fix (74138 B&C to GND)
Was able to use just RAM, just ROM or both - Works GREAT

Tested with a z180 CPU card, using a bq4017 nvRAM with RomWBW loaded @ 00000h ,!MREQ Jumpered, A19 to A19, A20 to Low
Second Rom image was loaded @ 10000h and you can switch to it by changing A20 to High - Works GREAT
(74138 chip not needed for 20bit 1-2M single chip operation)
One CHIP replaces three chips on the SC126 (2 EEPROMs and 1 RAM) and you can use up to 1M Byte of nvRAM if you want to...
Next I need to test with z280 

The Dual nvRAM board is a 512k to 4M - 20 to 32 Bit Address Linear Memory Board

The card supports 1 or 2 memory chips, ether one can be (nv)RAM or EEPROM
- 1 or 2 - 512k x 8 RAM (nv)RAM like the AS6C4008 / DS1250 / bq4015
- 1 or 2 - 512k x 8 EEPROM like the 39SF040
- 1 or 2 - 1M x 8 nvRAM like the DS1265 / bq4016
- 1 or 2 - 2M x 8 nvRAM like the DS1270 / bq4017
- 1 512k x 8 (RAM or EEPROM) and 1 1-2M x 8 nvRAM

The card should work with z180 / z280 / 80188 etc

- The optional 74LS682 is only used for 32 bit address decoding
- The optional 74LS139 is only used for 24 bit address decoding with 512k or 1M chips (spare half on an optional header)
- The optional 74LS138 is not used for 20 bit with one 1-2MB chip
- Using a nvRAM (DS1250) as U1, is a fast way to test BIOS updates (programmed by TL866)
- Using a nvRAM (DS1270) as U1, is a fast way to test two different BIOS updates 
  (programmed by TL866 using my 2M-NVRAM to 512K Adapter)
- Multiple cards can be used with a z280 to create up to 16MB system (MMU not yet supported by RomWBW)
- Cards can be addressed at any 512k boundary in a 4GB system (CPU that has a 32 Bit Address bus)

!MREQ Jumper (!RAM1 or !RAM2)
- One 1M or One half of a 2M NVRAM can be used with a 20 bit CPU by selecting !MREQ jumper 
- only 1 memory chip can be used
- A20 Jumper controls high of low half of 2M (allows for quick BIOS Change)
- TL866 can program the 1M or 2M NVRAM using a 36pin adapter and selecting DS1250 (512k at a time)
- TL866II can program the 1M NVRAM by selecting DS1265
- TL866II can program the 2M NVRAM using an adapter (A20 to +5 or GND) and selecting DS1265 (1M at a time)
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