November 1985
National Instruments
The Parallel Poll
After configuring the device, the GPIB-MAC now conducts a
parallel poll by calling
rpp. In
the previous example, where the
device was sent a configuration byte of hex
if the device’s ist bit
matches the S bit of hex
rpp
will return the value 04. Here, the
third least significant bit is set, corresponding to DIO line 3. (If any
other devices responded positively on other lines, those
corresponding bits would be set as well.)
Note that the controller may configure more than one device to
respond on the same data line, in which case the bits in the response
byte are set by the
of all the responses on that line.
Disabling Parallel Poll Response
The active controller may disable a specific device from responding
to a parallel poll by calling
ppu with the
device address as a
parameter.
ppu
sends the device the Parallel Poll Disable command
hex 70 (binary
01
1 1
0000),
which sets U to 1 to disable the device
from responding to a parallel poll.
To unconfigure all devices, the controller may call
ppu
with no
arguments, which sends PPU (parallel poll unconfigure, hex 15).
Example
A system has three line printers, two tape drives, one card reader,
and one PC on a system. The PC uses a GPIB-MAC to
communicate on the GPIB. All other devices are GPIB devices.
The PC is designated to be active controller, and all other devices
recognize this. Furthermore, all devices will set their ist bit to 1
when they are busy and 0 when they are free.
119
APPENDIX F PARALLEL POLLING
