17 Nov
2007
17 Nov
'07
9:59 p.m.
On Sat, Nov 17, 2007 at 12:40:25AM +0000, Tony Duell wrote:
Interesting. As I said, I've never seen one, in fact the only CBM GPIB
drives I've been inside are the 8050 and 8250LP.
I've never seen a 2031, but all the
GPIB-interfaces double drives contain
2 processors I think.
The 2031 is very much like a 1541, but with an IEEE-488 interface rather
than C= IEC. Prior to the 8050/8250, I think the arrangement was
one 6502 to talk to
the bus, and one 6504 to talk to the drives, but in other respects, the
same.
I wonder why they changed? I've not got the data book in front of me,
what was the address space of the 6504? The 8050 needs 8K, I think (4K
shared RAM + ROM + I/O devices). Did the earlier drives have less shared
RAM or something?
The control processor ROM is in one of those 6530
RRIOT chips, which
makes replaicng it a little problematic...
I have, I think, a full set of 2040 ROMs, including the right 6530, but
most of my pre-8050 drives were originally 2040s that were later upgraded
to the same ROMs as a 4040 (the only difference AFAIK is the label on the
outside).