Metrix GX1010 Notice De Fonctionnement page 126

5.1.2.3. ARC Interface Control Codes
All instruments intended for use on the ARC bus use the following set of interface control
codes. Codes between 00H and 1FH which are not listed here as having a particular
meaning are reserved for future use and will be ignored. Mixing interface control codes
inside instrument commands is not allowed except as stated below for CR and LF codes
and XON and XOFF codes.
When an instrument is first powered on it will automatically enter the Non- Addressable
mode. In this mode the instrument is not addressable and will not respond to any address
commands. This allows the instrument to function as a normal RS232 controllable device.
This mode may be locked by sending the Lock Non-Addressable mode control code 04H
(LNA). The controller and instrument can now freely use all 8 bit codes and binary blocks
but all interface control codes are ignored. To return to addressable mode the instrument
must be powered off.
To enable addressable mode after a instrument has been powered on the Set Addressable
Mode control code, 02h (SAM), must be sent. This will then enable all instruments
connected to the ARC 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 an instrument is sent a command it must be addressed to listen by sending the
Listen Address control code, 12H (LAD), 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 code 06H (ACK) before sending
any commands, The addressed instrument will provide this ACK. The controller should
time-out and try again if no ACK is received within 5 seconds.
Listen mode will be cancelled by any of the following interface control codes being
received:
12H
14H
03H
04H
18H
Before a response can be read from an instrument it must be addressed to talk by sending
the Talk Address control code, 14H (TAD) 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:
GX1010
LAD Listen Address followed by an address not
belonging to this instrument.
TAD Talk Address for any instrument.
UNA Universal Unaddress control code.
LNA Lock Non-Addressable mode control code.
UDC Universal Device Clear.
12H LAD Listen Address for any instrument.
14H TAD Talk Address followed by an address not
belonging to this instrument.
03H UNA Universal Unaddress control code.
04H LNA Lock Non-Addressable mode control code.
18H UDC Universal Device Clear.
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