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Remote Operation
RS232 Interface16
16-5
blocks but all interface control codes are ignored. To return to addressable mode the
instrument must be powered off.
To enable addressable mode after an instru
ment has been powered on the Set
Addressable Mode control code, 02H, must be sent. This will then enable all instruments
connected to the addressable RS232 bus to respond to all interface control codes. To
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 you can send a command to an instrument it m
ust 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. Thus 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 addressed 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
inform
ed that an instrument has accepted the listen address sequence and is ready to
receive commands. The controller will therefore wait for the addressed instrument to
provide the Acknowledge code, 06H, before sending any commands. The controller
should time-out and try again if no Acknowledge is received within 5 seconds.
Listen mode will be cancelled on receipt of any
of the following interface control codes:
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 m
ust 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 belongi
ng 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 co
mpleted 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 co
mmands 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
co
mmands; 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.
1.888.610.7664 sales@GlobalTestSupply.com
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