Instruction manual

62
Serial Poll Procedure
When serial poll procedure is initiated, a device is addressed to talk and
Active Controller sends Serial Poll Enable command (ATN line is low, because
addresses and GPIB command bytes are transferred over the interface).
The addressed device sends back to Active Controller a Status Byte (ATN line
is high, because data bytes are transferred over the interface).
Then, the Active Controller sends Serial Poll Disable command (ATN line is
low, because address and command bytes are transferred over the interface) to
end the serial poll sequence.
In order to obtain Status Byte from each device from bus, Active Controller
addresses the devices one by one.
Status Byte of each device must be analyzed. This makes serial poll procedure
to be relatively slow for large systems.
Interrogative Commands Over GPIB Interface
After receiving an interrogative command, when the response is ready to be
read, Message Available Bit (bit 4 of Status Byte Register) is set. Serial Poll
Enable command can be sent to read Status Byte.
Any other ommand (except Seria l Poll) clears the output buffer and the
response to the previous interrogative command is lost. In this case an error is
generated by the power supply (Err -410, Query interrupted) and MAV bit is
cleared.
In order to read the response to the previous interrogative command, the power
supply must be addressed as a Talker.
After the response is sent MAV bit is cleared.
MAV bit is also set when the power supply receives a command and it is not
able to execute it. Err -365, Timeout error message will be available in the
output buffer of the power supply.
When MAV bit is set, the power supply has a message to transmit to the Active
Controller. The power supply has to be addressed as a Talker in order to be able
to transmit the message.