Rice Lake SCT-30 - Manual (Page 15)

RS-485 Serial Connection 11
3.0 RS-485 Serial Connection
The instrument transmits via RS-485 serial port, according to a continuous one way
protocol or a querying protocol (MODBUS RTU). The division value will be between
0 and 200000 for load cell signal values between 0 and 10 mV.
For protocol setting, see Section 4.0.
3.1 Continuous One Way Transmission Protocol
The instrument transmits the number of divisions according to a continuous protocol
via the following string:
xxxxxxCRLF
where: xxxxxx = 6 division characters (48 – 57 ASCII).
CR = 1 carriage return character (13 ASCII).
LF
= 1 new line character (10 ASCII).
3.2 Modbus-RTU Protocol
The MODBUS-RTU protocol enables to manage the reading and writing of the
registers listed here below according to the specifications contained in the reference
document for this standard Modicon PI-MBUS-300.
The numerical data listed below are expressed in hexadecimal notation if preceded by
0x.
Modbus-RTU Data Format
The data received and transmitted via the MODBUS-RTU protocol has the following
format:
- 1 start bit
- 8 data bits, least significant bit sent first
- Parity none
- 1 stop bit
Of the controls available in the MODBUS-RTU protocol, only the READ HOLDING
REGISTER control may be used (code 0x03).
The interrogation frequency is linked with the preset communication rate (the
instrument will stand by for at least 3 bytes before beginning to calculate a possible
response).
Tot. bytes = 8
QUERY
Address Function Add. Reg. 1 No. register 2 bytes
A 0x03 0x0000 0x0002 CRC