Parallel Polling
Appendix F
GPIB-232CT User Manual
F-2
© National Instruments Corp.
busy and 0 when it is free, or vice versa. Consult your device
documentation for this information. With this information, the Controller
can configure devices according to the information desired.
Only the Active Controller can perform a parallel poll.
There are two steps to conducting a parallel poll: the following
configuration step, and the actual polling. The following paragraphs
describe these two steps.
Configuration
In the S Mode, the
ppc
function configures devices for parallel polls. For
example, if you want to configure a device at address 5 to respond on DIO
line 3 when the IST bit is 1, the programming message would be
ppc
5,3,1
. The GPIB-232CT takes the arguments
3,1
and constructs the
following parallel poll enable byte:
U
S DIO
lines
1-8
0 1 1 0 1 0 1 0
The value of this byte is hex 6A where:
U = 0
Enable
S = 1
Thus, when IST = 1 the device will assert DIO
line 3 (which corresponds to 010 in bits 0-2).
The
ppc
function sends the device's listen address, Parallel Poll Configure,
hex 6A, then unlisten. The Active Controller can configure itself to
respond to a parallel poll using
ppc
, also. This might be used in the case
where the GPIB-232CT is not the System Controller and the System
Controller does not have the capability to do the configuration. Since the
GPIB-232CT cannot be the Controller in the G Mode, the GPIB Controller
in your system must configure the GPIB-232CT in order to parallel poll it.
