CIRCUTOR CVM144 Series - Manual (Page 49)

----- Supply network analyzer CVM-144 ------ User's manual --- Page No. 48
11.4.- MODBUS © protocol
The CVM-144 analyzer can communicate by means of the MODBUS ©
protocol, as it is following described:
When the CVM-144 communicates with MODBUS protocol, it uses the RTU
mode (Remote Terminal Unit ). Each 8-bits byte in a message contains two 4-bits
hexadecimal characters.
The format for each byte in RTU mode is :
* Code : 8-bits binary, hexadecimal 0-9, A-F
Two hexadecimal characters
contained in each 8-bits field of the
message.
* Bits per Byte
: 8 data bits
* Error Check Field : Cyclical Redundancy Check ( CRC ) .
MODBUS FUNCTIONS:
FUNCTION 01 Reading of relay state
FUNCTION 3 or 4 Reading of n Words (16 bits-2 bytes). This function
permits to read all the electrical parameters of the
CVM-144. Each parameters is a 32-bits long, hence
two words are required to inquiry for a parameter.
FUNCTION 05 Writing one relay