With reference to my reply to Chuck's message, I've now dug out the
schematics.
The Sirius printer interface uses a 6522 VIA (at location U15L o nthe
mainboard). Port A is bufferec by a 75160 and fet ot the data pins on the
'Centronics' connector. Port B is used for the handshake lines, in
ascending bit order : DAV, EOI, REN, ATN, IFC, SRQ, NRFD, NDAC. Tese are
bufferec by a 75161, always in controller mode (DC is grounds). NRFD and
NDAC (o nthe 'host' side of the buffer) also go to CA1 and CA2
(respsecviely) of the VIA
The 'Talk' (buffer direction) line is controlled by PB0 of the 'system
VIA' at loccation U12L
The pinout of the 'Centroics' socket is :
DAV 1 19 Gnd
D0 2 20 Gnd
D1 3 21 Gnd
D2 4 22 Gnd
D3 5 23 Gnd
D4 6 24 Gnd
D5 7 25 Gnd
D6 8 26 Gnd
D7 9 27 Gnd
NRFD 10 28 Gnd
SRQ 11 29 Gnd
N/C 12 30 N/C
NDAC 13 31 N/C
J 14 32 NDAC
EOI 15 33 Gnd
Gnd 16 34 REN
FG 17 35 ATN
NC 18 36 IFC
A couple of non-obvious ones : 'J' (pin 14' is connected to ground via
the jumper E26-E27 (which is not normally fitted I think). FG is frame
ground (mains earth), not logic ground.
I/O chips i nthe Sirius seem ot be memory mammed for some odd reason. I
think the addresses are :
GPIB VIA : 1110 1xxx xxx0 001x rrrr
System VIA : 1110 1xxx xxx0 010x rrrr
where rrrr is selexts the VIA register in the obvious order.
-tony