Control Functions
PSI BOX PLUS+ Reference
PPE.
Sends Parallel Poll Enable Command.
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Purpose.
The secondary command Parallel Poll Enable is sent
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to the IEEE bus.
This command is used as part of a sequence to allow the
addressed listener to be assigned a data line for response to the
parallel poll command.
The PSI BOX asserts ATN and becomes the active
controller, then the IEEE command PPC, hex 060h decimal 96,
ORed with byte the user typed and is sent over the IEEE bus.
After the command has been sent the ATN remains true, PSI
BOX is the active controller.
The PPC command must precede the PPE command for a
correct bus sequence to be performed. The PPE command is
used to tell the addressed listener which particular data line it is
to use when responding to a parallel poll, the PPE command
also tells the addressed device whether to assert the line when it
requires service or to assert the line when it does not require
service.
The PPE command has the bit value %0110sppp. Here s is
the sense of response bit and ppp is the data line assigned to the
device.
The sense information is in bit 3 (decimal 8).
If bit 3=0 then assert line when the device’s individual status bit,
IST, is zero.
If bit 3=1 then assert line when the device’s IST is one.
The data line is assigned using bits 0-2.
If bits= 000, decimal 0, then data line 0
If bits= 001, decimal 1, then data line 1
If bits= 010, decimal 2, then data line 2
If bits= 011, decimal 3, then data line 3
If bits= 100, decimal 4, then data line 4
If bits= 101, decimal 5, then data line 5
If bits= 110, decimal 6, then data line 6
If bits= 111, decimal 7, then data line 7
The sense value and the data line value are logically OR’d
together with the PPE command ($60) and sent to the bus after
PPC with ATN true.
Chapter 8
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