Chapter 5
Programming Considerations
© National Instruments Corporation
5-25
GPIB-1014 User Manual
2. Send the GPIB UNL message to unaddress all GPIB Listeners.
3. Send the listen address of the first device to be configured.
4. Send the GPIB PPC message to all devices followed by the PPE message for that device.
5. Repeat from the second step (UNL) for each additional device.
Follow the same procedure to disable polling with PPD (for example, when changing responses
during reconfiguration).
Responding to a Parallel Poll
Before the GPIB-1014 can be polled by the CIC, the TLC must be configured either locally by
your program at initialization time or remotely by the CIC. Configuration involves the
following:
•
Enabling the TLC to participate in polls
•
Selecting the sense or polarity of the response
•
Selecting the GPIB data line on which the response will be asserted when the CIC issues the
IDY message
With remote configuration (PP1), the TLC interprets the configuration commands received from
the CIC, without any software assistance or interpretation from your program. With local
configuration (PP2), the three actions listed above must be explicitly handled in the software by
writing the appropriate values to the U, S, and P3 to P1 bits of the PPR. Refer to the PPR
description in Chapter 4 for more information.
Once the PPR is configured, all that remains for your program is to determine the source and
value of the local individual status (ist) message. If the ISS bit in the AUXRB is 0, ist is set and
cleared via the Set and Clear Parallel Poll auxiliary commands. If ISS is 1, ist is set if the
Service Request function of the TLC is in the Service Request State (SRQS) and the TLC is
asserting the GPIB SRQ signal line and cleared otherwise. Consequently, setting ISS ties the
Parallel Poll function to the Service Request function and also to the Serial Poll process.
As explained under the Conducting a Serial Poll section earlier in this chapter, which of the 16
possible responses that is transmitted by the TLC during a Parallel Poll is a function of the value
of ist and the configuration of the TLC. The GPIB system integrator must decide what ist
indicates and what configuration is used. The response can be changed dynamically during
program execution by changing the value of ist and, when remote configuration is used, by
reconfiguration.