Control Functions
PSI BOX PLUS+ Reference
PPD.
Sends Parallel Poll Disable.
_____
________________________
Purpose.
The secondary command Parallel Poll Disable is
__________
sent to the IEEE bus.
The PPD command is used as part of a sequence to
prevent the particular addressed device from responding to
parallel polls. The previously assigned data lines is remembered.
The PSI BOX asserts ATN and becomes the active
controller, then the IEEE command PPD, hex 070h decimal 112,
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 PPD command for a
correct bus sequence to be performed. The PPD command is
used to tell the addressed listener that it must no longer respond
to the controller’s parallel poll command. Though unable to
respond the device remembers its parallel poll line assignment
made by the previously issued PPC and PPE commands,
probably using the CONFIGURE instruction.
The PPD command has been included for completeness
only, it is advised that the DISABLE command be used to
disable the response of a device to Parallel Poll.
The PPE command can also be sent by using CMD 112 or
CMD 240 or SEC 16
Format.
PPD
_________
Params.
None.
_________
Returns.
None.
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Example.
________
_
BUS PPD
recommended sequence (if not using DISABLE )
BUS UNT UNL LISTEN 1 PPC PPD UNL
Bus Activity.
___________
_
assert ATN if not already so
PPC
recommended sequence (if not using DISABLE)
Chapter 8
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