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Chapter 6
Parallel Polling
Although parallel polling is not widely used, it is a useful method for obtaining
the status of more than one device at the same time. The advantage of parallel
polling is that a single parallel poll can easily check up to eight individual
devices at once. In comparison, eight separate serial polls would be required to
check eight devices for their serial poll response bytes. The value of the
individual status bit (ist) determines the parallel poll response.
Implementing a Parallel Poll
You can implement parallel polling with either NI-488 functions or NI-488.2M
routines. If you use NI-488.2M routines to execute parallel polls, you do not
need extensive knowledge of the parallel polling messages. However, you
should use the NI-488.2M functions for parallel polling when the GPIB board is
not the Controller and must configure itself for a parallel poll and set its own
individual status bit (ist).
Parallel Polling with NI-488.2 Routines
Follow these steps to implement parallel polling using NI-488.2 routines. Each
step contains example code.
1.
Configure the device for parallel polling using the PPollConfig
routine, unless the device can configure itself for parallel polling. The
following example configures a device at address 3 to assert data line 5
(DIO5) when its ist value is 1.
#include "decl.h"
char response;
Addr4882_t AddressList[2];
/* The following command clears the GPIB.
SendIFC(0);
/* The value of sense is compared with the ist bit of
the device and determines whether the data line is
to be asserted or unasserted.
PPollConfig(0,3,5,1);
© National Instruments Corp.
GPIB Programming Techniques
6-9
NI-488.2M SRM for OS/2
*/
*/
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