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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. The controller should time-
out and try again if no Acknowledge 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 addressable RS232 mode.
Full List of Addressable RS232 Interface Control Codes
02H
Set Addressable Mode.
03H
Universal Unaddress control code.
04H
Lock Non-Addressable mode control code.
06H
Acknowledge that listen address received.
0AH
Line Feed (LF); used as the universal command and response terminator.
0DH
Carriage Return (CR); formatting code, otherwise ignored.
11H
Restart transmission (XON).
12H
Listen Address - must be followed by an address belonging to the required instrument.
13H
Stop transmission (XOFF).
14H
Talk Address - must be followed by an address belonging to the required instrument.
18H
Universal Device Clear.
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