Specifications

Open CTM (Revision D)

174

MODBUS Messages

Bit 2 represents output #3

Bit 3 represents output #4

Bit 4 represents output #5

Bit 5 represents output #6

11.4 Read Analog Inputs

In MODBUS term this is called “read input registers” and has function code 0x04.

Request message: 0xII 0x04 0xSS 0xSS 0xNN 0xNN 0xZZ 0xZZ

Where:

0xII is the modem’s assigned MODBUS ID

0xSS 0xSS is the start address for reading registers

0xNN 0xNN is the number of registers to read

0xZZ 0xZZ is the CRC checksum for this message

Example:

To read all the modem’s six analog input values:

0xII 0x04 0x00 0x00 0x00 0x06 0xZZ 0xZZ

Response message:

0xII 0x04 0x0C 0xH1 0xL1 0xH2 0xL2 0xH3 0xL3 0xH4 0xL4 0xH5 0xL5 0xH6 0xL6

0xZZ 0xZZ

Where:

0xHn is the high byte for analog input n

0xLn is the low byte for analog input n