Fluke 281 User Manual page 297

return to non-addressable mode the Lock Non-Addressable mode control code must be
sent which will disable addressable mode until the instruments are powered off.
Before an instrument is sent a command it must be addressed to listen by sending the
Listen Address control code, 12H, followed by a single character which has the lower 5
bits corresponding to the unique address of the required instrument, e.g. the codes A-Z or
a-z give the addresses 1−26 inclusive while @ is address 0 and so on. Once addressed to
listen the instrument will read and act upon any commands sent until the listen mode is
cancelled.
Because of the asynchronous nature of the interface it is necessary for the controller to be
informed that an instrument has accepted the listen address sequence and is ready to
receive commands. The controller will therefore wait for Acknowledge code, 06H,
before sending any commands. The addressed instrument will provide this Acknowledge
code. The controller should time out and try again if no Acknowledge code is received
within 5 seconds.
Listen mode will be cancelled by any of the following interface control codes being
received:
12H Listen Address followed by an address not belonging to this instrument.
14H Talk Address for any instrument.
03H Universal unaddress control code.
04H Lock Non-Addressable mode control code.
18H Universal Device Clear.
Before a response can be read from an instrument it must be addressed to talk by sending
the Talk Address control code, 14H, followed by a single character which has the lower 5
bits corresponding to the unique address of the required instrument, as for the listen
address control code above. Once addressed to talk the instrument will send the response
message it has available, if any, and then exit the talk addressed state. Only one response
message will be sent each time the instrument is addressed to talk.
Talk mode will be cancelled by any of the following interface control codes being
received:
12H Listen Address for any instrument.
14H Talk Address followed by an address not belonging to this instrument.
03H Universal Unaddress control code.
04H Lock Non-Addressable mode control code.
18H Universal Device Clear.
Talk mode will also be cancelled when the instrument has completed sending a response
message or has nothing to say.
The interface code 0AH (LF) is the universal command and response terminator; it must
be the last code sent in all commands and will be the last code sent in all responses.
The interface code 0DH (CR) may be used as required to aid the formatting of
commands; it will be ignored by all instruments. Most instruments will terminate
responses with CR followed by LF.
The interface code 13H (XOFF) may be sent at any time by a listener (instrument or
controller) to suspend the output of a talker. The listener must send 11H (XON) before
the talker will resume sending. This is the only form of handshake control supported by
the addressable RS232 mode.
17
Remote Operation
RS232 interface
17-5