Product Manual

291, 292, 294
Users Manual
RX
1
1
2
3
4
5
6
7
8
9
2
3
4
5
6
7
8
9
DCD
RX
TX
DTR
GND
DSR
RTS
CTS
RI
TX
GND
9-WAY D
MALE
9-WAY D
FEMALE
123456789
TX RX TXIN RXOUT
UP TOWARDS
CONTROLLER
DOWN TOWARDS
OTHER INSTRUMENTS
INSTRUMENT
CONNECTOR
9-WAY D
MALE
shc0012f.emf
Figure 17-3. RS232 Daisy-Chain Connector Wiring
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
Parity: None
Stop Bits: 1
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
17-4