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Principles of Operation
~a
PORT INTERFACE
The parallel port I/O (via connector JI) on the Multi-
module board consists of three 8-bit ports that may
be configured in one of several modes, as listed in
table 4-2. The eight bits of Port A and eight bits of
Port B must be configured as units to either input or
output mode, but Port C may be broken into two
groups of four, either of which can be used in input
and/or output mode.
Data I/O through Port A passes through two 8226
Bidirectional Bus Drivers
(VI
and
V2)
which control
iSBX 350
the direction of data flow according to the condition
of DIEN/, the signal on jumper post E2. When
DIEN/ is low, data flows from the PPI to the port
data lines. Conversely, when DIEN/ is high, data
flows from the port data lines to the PPI.
Four I4-pin DIP sockets are provided for user-
supplied line driver/receiver device installation onto
the Port B and Port C data lines. The type of line
driver/receiver device is determined by the applica-
tion.
Table 4-2. Mode Definition Summary Table
Mode 0
Mode 1
Mode 2
PortlBlt
IN
OUT
IN
OUT
GROUP A ONLY
PAa
IN
OUT
IN
OUT
Bidirectional
PA,
IN
OUT
IN
OUT
Bidirectional
PA
2
IN
OUT
IN
OUT
Bidirectional
PA
3
IN
OUT
IN
OUT
Bidirectional
PA
4
IN
OUT
IN
OUT
Bidirectional
PAs
IN
OUT
IN
OUT
Bidirectional
PAs
IN
OUT
IN
OUT
Bidirectional
PA
7
IN
OUT
IN
OUT
Bidirectional
PS a
IN
OUT
IN
OUT
-
PS,
IN
OUT
IN
OUT
-
PB
2
IN
OUT
IN
OUT
-
PB
3
IN
OUT
IN
OUT
-
PB
4
IN
OUT
IN
OUT
-
PBs
IN
OUT
IN
OUT
-
PBs
IN
OUT
IN
OUT
-
PB
7
IN
OUT
IN
OUT
-
PC a
IN
OUT
INTRa
INTRa
110
PC,
IN
OUT
IBFa
OBFe!
110
PC
2
IN
OUT
STBal
ACKei
1/0
PC
3
IN
OUT
INTRA
INTRA
INTRA
PC
4
IN
OUT
STBAI
1/0
STBAI
PC s
IN
OUT
IBFA
110
IBFA
PC s
IN
OUT
1/0
ACKAI
ACKAI
PC
7
IN
OUT
1/0
OBFAI
OBFAI
4-2
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