Re: cbm 256-80 ROMS, PLA and 8088 co-processor.

From: Charlie (
Date: 2009-03-09 00:15:11

Hi Bill,
  I am certain that my machine boots up properly with the 256 roms and dos 
board installed.  I can double check tomorrow.
----- Original Message ----- 
From: "B Degnan" <>
To: <>
Sent: Sunday, March 08, 2009 7:38 PM
Subject: cbm 256-80 ROMS, PLA and 8088 co-processor.

> To anyone who cares about the B Series 8088 Co-processor..
> I have strong circumstantial evidence that the program space used by the 
> original CBM 8088 co-processor (intended for but not officially sold for 
> the B Series) conflicts with the space that the CBM 256-80 BASIC ROMS use, 
> and therefore a stock CBM 256-80 will not work with the 8088 co-processor. 
> That explains why the 2 256's with the co-processors I have came with B128 
> BASIC ROMS in them. I will bet that no one with a 8088 co-processor and 
> 256 BASIC ROMS will be able to get it to work properly.  By swapping ROMS 
> with another working system and/or working parts I learned of this 
> situation. Only when I had the following ROMS in a hi-profile B Series 
> system would the co-processor work:
> 901243-02 (B128 BASIC)
> 901242-02 (B128 BASIC)
> 901244-03 (probably not important KERNAL)
> Both the HIBOY PLA 906114-05 and 906114-04 work with the 8088 co-proc.
> To reiterate - "common knowledge" is incorrect, it's not the PLA that 
> makes a hi-profile board compatible with the 8088 co-processor, it's 
> probably the BASIC ROMS (you can't use the stock CBM 256-80 ROMs).
> I would need to dump the program listing of the 8088 co-processor to 
> confirm this.  If there is a strong interest I will attempt to pull it 
> down, time permitting.  This is one of those things I will do eventually, 
> and when complete I will share with this group.
> Bill Degnan
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