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CPU
2i10g
Table 4-1.
Printer Control Signals
Bit Number
Centronics
Data Products
0
Data Strobe-
Data Strobe
I
Not Used
Not Used
2
Not Used
Not Used
3
Not Used
Not Used
CPU
4.3.2.
Printer
Status Inputs:
The printer status
parallel
inputs
to
the
PIO are buffered by UID3 and input at the A
port bits A4 through A7.
The jumper
El3
to
El4
puts
an
active low signal on the BSTB- strobe input to the PIO after
the signal is passed through the buffer U12.
At
the
same
time,
the
signal is applied to the A7 bit input of Port A.'
This is the Centronics Acknowledge- signal that the
printer
is ready for data transmission.
The positive active signal Data Demand is the Data
Products
counterpart
of
this
signal which is inverted by jumpering
El4 to EIS.
A printer Busy status is received at A4
as
an
active
positive
signal, after being inverted by UII,and is
the same for both printer interfaces.
The AS and A6
inputs
remain
high
for both high and low input signals due to the
+SV pull-up resistors RIg and
R20.
Table
4-2
shows
the
printer status signals for both the Centronics and Data Pro-
ducts printer interface.
Table 4-2.
-Printer Status Signals
Bit Number
Centronics
Data Products
4
Busy-
Busy-
S
Select
Onl ine
n
Fault-
Interface Valid
7
Acknowledge-
Data Demand
4.4.
Serial Input/ Output
The
Z80B
SIO/2
serial
input/output
supplies
two
fully
independent
full-duplex asynchronous serial data communica-
tions channels.
Four S10/2 devices on the System
8000
CPU
board
are the eight serial (SIO) input/output channels that
support ,with additional hardware, the RS-232C standard
for
serial communications.
4-5
21log
4-5
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