National Instruments NI-488.2, Руководство пользователя

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Chapter 7 NI-488.2 Programming Techniques
© National Instruments Corporation 7-19 NI-488.2 User Manual for Windows
Parallel Polling with Multi-Device NI-488.2 Calls
Complete the following steps to implement parallel polling the using
multi-device NI-488.2 calls. Each step contains example code.
1. Configure the device for parallel polling using the
PPollConfig
call,
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-32.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 asserted.*/
PPollConfig(0,3,5,1);
2. Conduct the parallel poll using
PPoll
,
store the response, and check
the response for a certain value. In the following example, because
DIO5 is asserted by the device if
ist
is 1, the program checks bit 4
(hex 10) in the response to determine the value of
ist
.
PPoll(0, &response);
/* If response has bit 4 (hex 10) set, the ist bit
of the device at that time is equal to 1. If
it does not appear, the ist bit is equal to 0.
Check the bit in the following statement. */
if (response & 0x10) {
printf("The ist equals 1.\n");
}
else {
printf("The ist equals 0.\n");
}
3. Unconfigure the device for parallel polling using
PPollUnconfig
, as
shown in the following example. In this example, the
NOADDR
constant
must appear at the end of the array to signal the end of the address list.
If
NOADDR
is the only value in the array, all devices receive the parallel
poll disable message.
AddressList[0] = 3;
AddressList[1] = NOADDR;
PPollUnconfig(0, AddressList);