The Parallel Poll - National Instruments GPIB-MAC User Manual

November 1985
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 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.
There are two steps to conducting a parallel poll: the configuration
step and the actual polling. The following paragraphs describe
these two steps.
Configuration
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
constructs the following parallel poll enable byte:
11
The value of this byte is hex 6A where
U = 0, enable
S = 1,
The ppc function sends the device's listen address, the Parallel Poll
Configure command, hex 6A, then the Unlisten command. The
active controller can configure itself to respond to a parallel poll
using
MAC is not the system controller and the system controller does not
have the capability to do the configuration. Since the GPIB-MAC
cannot be the controller, the GPIB controller in your system must
configure the GPIB-MAC in order to parallel poll it.
118 APPENDIX F = PARALLEL POLLING
U
1
when ist = 1 the device will assert DIO
line3 (which corresponds to 010 in bits O-2).
This might be used in the case where the GPIB-
S