© National Instruments Corp.
F-1
GPIB-232CT User Manual
Appendix F
Parallel Polling
A GPIB Controller can use parallel polling to obtain information from
several devices on the GPIB in one operation. The Controller polls
configured devices and reads back a single response byte that contains one
bit of information from each device. From this information, the Controller
can determine which devices need servicing.
Operation
A device is configured by sending it its listen address and a parallel poll
enable (PPE) message. There are 16 possible PPE messages: hex 60
through hex 6F. The bits in the PPE message have the following meaning:
U
S DIO
lines
1-8
0 1 1 X X X X X
U
When 0 (hex 6X), parallel poll is enabled. When 1 (hex
7X), parallel poll is disabled.
S
When the device's IST (individual status) bit matches the S
bit, the device will set the appropriate data line. Hex 60
through hex 67, set S to 0; hex 68 through hex 6F, set S
to
1.
DIO The
value
n
in bits 0-2 corresponds to one of the DIO
lines 1 through 8, where
n
corresponds to DIO line
n+1
.
Thus, a value of 2 (binary 010) corresponds to DIO line 3.
The circumstances under which a device sets its IST bit are specific to that
device. For example, a device might always set the IST bit to 1 when it is
