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Chapter 4 Remote Interface Reference
The SCPI Status Registers
106
Caution
The IEEE-488 standard does not ensure synchronization between your bus
controller program and the instrument. Use the
*OPC?
command to
guarantee that commands previously sent to the instrument have completed.
Executing a serial poll before a
*RST, *CLS,
or other commands have
completed can cause previous conditions to be reported.
Using *STB? to Read the Status Byte
The
*STB?
(Status Byte query) command is similar to a serial poll but it is
processed like any other instrument command. The
*STB?
command returns
th e sa me r es ul t a s a se ri al pol l bu t t he “r equ est se rv ic e” bi t (b it 6 ) is not cleared.
The
*STB?
command is not handled automatically by the IEEE-488 bus
interface hardware and will be executed only after previous commands have
completed. Polling is not possible using the
*STB?
command. Executing the
*STB?
command does not clear the Status Byte summary register.
Using the Message Available Bit (MAV)
You can use the Status Byte “message available” bit (bit 4) to determine when
data is available to read into your bus controller. The power supply
subsequently clears bit 4 only after all messages have been read from the
output buffer.
To Interrupt Your Bus Controller Using SRQ
1
Send a device clear message to clear the power supply’s output buffer (e.g.,
CLEAR 705
).
2
Clear the event registers with the
*CLS
(clear status) command.
3
Set up the enable register masks. Execute the
*ESE
command to set up the
Standard Event register and the
*SRE
command for the Status Byte.
4
Send the
*OPC?
(operation complete query) command and enter the result to
ensure synchronization.
5
Enable your bus controller’s IEEE-488 SRQ interrupt.