12
Checking 5520A Status
(cont)
Service Request (SRQ) Line
IEEE-488
Bus control line that asserts to notify
the controller that it requires some type of service.
RS-232
Sends the SRQSTR string over the serial
interface when service is required.
Service Request Enable Register (SRE)
The SRE enables or masks the bits of the Serial
Poll Status Byte. The SRE is cleared at power up.
Output Queue
Whenever a query is processed, the output queue
is loaded. If the queue is empty, the Calibrator
does not respond to the INPUT statement. The
Message Available (MAV) bit in the Serial Poll
Status Byte is 1 if there is something in the output
queue and 0 if the output queue is empty. The
output queue contains a maximum of 800
characters.
Error Queue
Whenever a command error, execution error, or
device-dependent error occurs, its error code is
placed in the error queue where it can be read by
the ERR? command. The error queue contains a
maximum of 16 entries.