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All instruments on the interface must be set to the same baud rate and all must be powered on,
otherwise instruments further down the daisy chain will not receive any data or commands.
The other parameters are fixed as follows:
Start Bits: 1
Data Bits: 8
RS232 Character Set
Because of the need for XON/XOFF handshake it is possible to send ASCII coded data only;
binary blocks are not allowed. Bit 7 of ASCII codes is ignored, i.e. assumed to be low. No
distinction is made between upper and lower case characters in command mnemonics and they
may be freely mixed. The ASCII codes below 20H (space) are reserved for addressable RS232
interface control. In this manual 20H, etc. means 20 in hexadecimal
Addressable RS232 Interface Control Codes
All instruments intended for use on the addressable RS232 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. 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 an instrument 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 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.
28
Parity: None
Stop Bits: 1
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