36
command:
:SYSTem:COMMunicate:GPIB:ADDRess
Setting the device to address 31 puts it in the 'off-bus' state. In this state it will not respond to
messages on the GPIB. If the device is in the REMS when set to address 31, an internal 'return-to-local'
command will be given, setting the device to the LOCS. If the device is in the RWLS, the 'return-to-local'
command is ignored, and the device remains in the RWLS. The only way to then re-establish
communication with the device over the GPIB is to cycle the power, and to then change the address to
that required from the front panel.
4.5
Message Exchange Protocol
The device decodes messages using the Message Exchange Protocol (MEP) defined in IEEE 488.2. The
following functions implemented in the MEP must be considered:
The Input Buffer
The device has a 256-byte long cyclic input buffer. Decoding of remote messages begins as soon as the
input buffer is not empty, that is, as soon as the controller has sent at least one byte to the device.
Should the input buffer be filled up by the controller faster than the device can remove the bytes and
decode them, the bus handshake is not completed until room has been made for more bytes in the
buffer. This prevents a fast controller from overrunning the device with data.
If the user has sent part of a Program Message, but not the Program Message Terminator, and he
wishes to abort the message decoding and execution, the Device Clear command may be sent, or front
panel operation resumed (in REMS only).
The Output Queue
The device has a 100-byte long output queue in which it stores response messages for the controller to
read. If at the time a response message is formatted the queue contains previously formatted response
messages, such that there are not enough places in the queue for the new message, the device will put
off putting the message in the queue until there is place for it.
The Status Byte MAV bit, when set, indicates that part or all of a response message is ready to be read.
Response Messages
The device sends a Response Message in response to a valid query. All queries return a single Response
Message Unit. In only one case is the Response Message generated when the response is read (as
opposed to when the response is parsed), and this is when querying Arbitrary Waveform data. All other
queries generate the Response Message when they are parsed.
Coupled Commands
Coupled Commands are either commands whose execution validity depends on the value of other
parameters, or commands whose execution changes the value of another parameter. The execution of
commands designated as being coupled is deferred until all other commands in the same Program
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