HP 3468A - Service Request (SRQ) Functionality

SERVICE
REQUEST
(SRO)
Another important feature of the 3468A is you can program it to interrupt the
controller when certain conditions are met. Of course, the controller must also be
programmed to respond to the interrupt. The Require Service (SRO) message is us-
ed to implement this and is independent of all other HP-IL activity. The 3468A
MUST BE PROGRAMMED for the interrupt before the interrupt will take place. The
following list gives the possible causes of interrupt that the 3468A can be pro-
grammed for.
1. Power-on/ Reset. The 3468A will interrupt the controller when the 3468A
power is turned on.
2. CAL Failure. The 3468A will interrupt the controller if an attempted calibra-
tion failed.
3. Front Panel Keyboard. You can use the front panel SRO key on the 3468A
to interrupt the controller.
4, Hardware Error. If a hardware error occurs, the controller would be inter-
rupted.
5. Syntax Error. If the controller sent an invalid instruction, the 3468A would
interrupt the controller.
6. Data Ready. The 3468A would interrupt the controller after each completed
measurement.
7. Invalid Function and Range combinations.
How to use SRO
When the Require Service message (SRQ) is sent, the computer must determine
first which instrument is requesting service. This is done by conducting a SERIAL
POLL (SPOLL) of every device on the loop which is capable of requesting service.
When an instrument is polled, it responds by sending a “STATUS BYTE” which
indicates whether it requires service, and if so, the nature of the request. If the
Status Byte for the instrument polled indicates that it was not requesting service,
the computer would continue to poll the other instruments on the loop until the
proper one is located. This, of course assumes that the controller has been pro-
grammed to respond to the SRQ interrupt.
The Status Byte together with the Service Request (SRQ) Mask determine when
the Require Service (ROS) bit is to be set. Setting ROS causes SRO to be sent on
the HP-IL. A Serial Poll of the 3468A will clear SRO and it will remain clear until
another reason for setting ROS occurs. ROS on the other hand, is set if one or
more corresponding bits in the Status Byte and SRO Mask are both set. RQS is
cleared whenever all corresponding bits are not both set. A Serial Poll then, may
cause RQS to be cleared but not in all cases. Bits 2, 4, 5, and 7 are cleared with
a Serial Poll.
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