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

From: B Degnan (billdeg_at_degnanco.com)
Date: 2009-03-08 23:38:51

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

       Message was sent through the cbm-hackers mailing list

Archive generated by hypermail pre-2.1.8.