HP 8901B Operation And Calibration Manual

Model 8901B Operation
Status Byte
Overview. The Status Byte bits 0-5 reflect the status of the unmasked Instrument Conditions. Refer
to Table
3-9, “SRQ Mask and Status Byte Bit Descriptions” for bit definitions. At power-up and
Instrument Preset, the only Status Byte bit which
is unmasked is the HP-IB Error Code bit.
The RQS bit (bit 6) is automatically set if any other bit in the Status Byte is set true. When the RQS
bit
is set, the Service Request message is sent. The front-panel SRQ annunciator turns on at the next
front-panel display update. Once any Status Byte bit has been set,
it remains set until the Status Byte
is read.
If one of these Instrument Conditions occurs, while it is masked by the SRQ Mask, NEITHER the
Status Byte bit corresponding
to the condition NOR the RQS bit will be set, and the Service Request
message will not be sent.
Reading the Status Byte
NOTE
a A Status Byte Bit that is not unmasked by the SRQ Mask will
ALWAYS read
as a zero when the Status Byte is read. Only an
unmasked bit can be read
as a one, and then only if its initiating
Instrument Condition occurs AFTER it
is unmasked.
a Reading the Status Byte is, the only accurate way to determine the
condition of the SRQ bus line (Service Request message). The SRQ
annunciator is only updated
as the front panel is updated. It is NOT
tied directly to the SRQ bus line.
a The Modulation Analyzer cannot alter the Status Byte while in serial
poll mode; therefore,
it is not possible to continually poll the Status
Byte while waiting for a condition to cause a bit to be set.
a Reading Status of non-existent devices (HP-IB addresses not in use)
will hang
the HP 8901B HP-IB and requires a Device Clear (DCL)
message to clear the bus.
The Status Byte can be read using a serial poll, only if the instrument sends a Service Request Message.
Only those bits which are unmasked by the SRQ Mask can be read accurately.
Talk Status Only causes the instrument to only output the Status Byte. Refer to “TALK and LISTEN
Status Descriptions” for more information.
3-31

HP 8901B Specifications

General

Brand	HP
Model	8901B
Category	Measuring Instruments
Language	English