9 COMMUNICATION
9.1 Communication
Protocol
CL551
is equipped with a RS232 bi-directional , half-duplex interface as standard.
Baud rate is set at 9600 baud as default. You can modify it through keyboard selecting following rate : 300, 600, 1200,
2400, 4800, 9600 and 19200 baud. Transmission parameters are 8 bit length, no parity and 1 bit stop. Address can be
modified through keyboard and it is set 1 as default. RS232 interface connector is a 9 pin DB9 male connector.
Cable connection to a standard personal computer as follows :
9 pin CL551 9 pin PC connector
25 pin PC connector
2 ----------------------------------------> 3 --------------------------> 2
3 ----------------------------------------> 2 --------------------------> 3
5 ----------------------------------------> 5 --------------------------> 7
Communication protocol is based on Answer to Request system.
CL551
will answer only if you sent a Request to it.
There are two kind of request :
RVAR to read a variable.
WVAR to set a variable.
9.2
Reading a variable
The instruction to read a variable has to be an ASCII code composed as follows :
$ character
Instrument Address
RVAR request string
Variable Index
Blank space
Carriage Return
For example, if the set point has to be read (Variable index = 0), supposing the instrument address to be 1:
$1RVAR0 \r
ASCII
code
$ 1 R V A R 0 \r
HEX
$
code
24 31 52 56 41 52 30 20 0D
The answer of the
CL551
will be as follows
* character
Carriage return
* character
Instrument Address
Answer string
Carriage Return
For example if set point is 50.5 °C , supposing the instrument address to be 1:
ASCII
code
* \r
* 1 S P
: 0 0 5 0 . 5 \r
HEX $
code
2A 0D
2A 31 20 53 50 20 20 3A 20 30 30 35 30 2E 33 0D
List of Variable Index available
Variable Index
Actual Setpoint
0
Ramp : ON /OFF
1
22
