ReadStatus and PPoll Board Level GPIB Functions Hardware: GPIB
Problem: What are the differences between the ReadStatus function and the PPoll function? How does each work?Solution: The ReadStatus (SPoll) function is used to obtain the entire status byte of an instrument. The ReadStatus function first sends out a low level Serial Poll Enable (SPE) command on the GPIB bus. The function then issues a My Listen Address 0 and a My Talker Address X, where X is the instrument address you specify using the address input on the function. The instrument at address X will then send its entire status byte back, which will be sent to the output on the serial poll response connector on the function.
Most instruments have one byte that serves as the official status byte. The ReadStatus function will then end the serial poll by sending out a low level Serial Poll Disable (SPD) on the bus.The AllSpoll function can be used to return the status bytes of multiple instruments on the GPIB bus. It works essentially the same way as the ReadStatus function, except that you will specify more than one instrument address.The PPoll function can be used to poll the individual status (IST) bit of up to eight instruments at once. Collectively, all of these eight IST bits are grouped together into a single byte. The PPollConfigfunction is used to designate which line the IST bit is placed on and which instruments will participate in a parallel poll. There is not a way to return a specific bit of a status byte, and the PPollConfig function will not work in conjunction with the ReadStatus function.Related Links: Developer Zone Tutorial: Parallel Polling with NI-488.2 Software KnowledgeBase 33DA1C2Y: How Can I Handle Service Request and Serial Polling When Using Multiple Logical Devices? Developer Zone Tutorial: Serial Polling and SRQ Servicing with NI-488.2 Software and LabVIEW Product Manuals: NI-488.2 User Manual Attachments:
Report Date: 07/27/2004 Last Updated: 03/05/2008 Document ID: 3BQC1IQ8 |
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