From: fachat (afachat_at_gmx.de)
Date: 2005-04-08 13:19:30
On Thu, Apr 07, 2005 at 08:09:29PM +0200, Patrycjusz R. Ćogiewa wrote:
> Does anyone know what function has the PCR (mapped at $1C0C) of VIA2
> inside 1541?
The PCR is the "Peripheral Control Register" of the VIA6521. It controls
the behaviour of the hardware pins CA1, CA2, CB1 and CB2.
Pleas see http://www.funet.fi/pub/cbm/documents/chipdata/
To see what the pins do, look at the schematics of the VC1541, at
http://www.funet.fi/pub/cbm/schematics/drives/new/1541/tech
for example in the file 1541-33b-right.gif.
IIRC VIA2 is the drive controller VIA, so, the PCR controls the lines
CB1 - not connected
CB2 = MODE -> Output Enable (OE) of Gate Array
CA1 = BYTE -> Gate Array Pin BYTE, also connected to S.O. of the 6502
CA2 = SOE -> Gate Array Pin SOE
IIRC MODE determines whether data is written to or read from the
drive head, BYTE is an input that determines whether the read or
write of a byte is finished. And SOE I cannot remember.
If you really want to know the exact meaning, you could analyze
the drive schematics of the early (long board) VC1541 (e.g. in
file 1541-35.gif under the abovementioned URL) where there
was no Gate Array, but the logic was done in discrete logic (standard
TTL chips). I did this once, but this is is something like editing
sendmail.cf directly - you do it once and never again :-)
André
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