After a device initiates a service request (SRQ), the active controller normally performs polling. Polling can be performed serially or in parallel.
Serial polling is usually performed as follows:
After a device initiates the service request, the controller performs the following actions in sequence:
Addresses the device as a talker.
Sends the SPE command to set up serial polling mode.
Waits for the device in question to send its response to the poll.
Sends the SPD command to disable serial polling mode.
Sends the UNT command to "untalk" the device.
For information on the meaning of a particular instrument’s response to the serial poll, see the instrument’s user documentation. Usually bit #6 in the serial poll byte is set to 1 when SRQ is asserted.
With parallel polling, devices on the system can be polled simultaneously. Using this approach, each device is assigned one of the eight data lines. If a device requires service, it sets its data line to true when being polled. Parallel polling is initiated when the controller asserts ATN and EOI simultaneously.
For additional information on the IEEE-4888 standard, contact:
The Institute of Electrical and Electronics Engineers, Inc.
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