dS1242
dS1242 User Manual v4.10
Modbus commands
The modbus command set accepts a subset of the standard Modbus-TCP frames as defined in
Modbus protocol Specification and
MODBUS Messaging on TCP/IP Implementation Guide V1.0b
Functions 1, 4, 5 & 15 are supported along with error codes 1, 2 & 3 should they occur.
The UI (Unit Identifier) should be 0x01 to access this module.
Function 01 (0x01) Read Coils
This function reads back the 2 relays as coils 1-2 and also the 4 inputs as coils 41-44.
Function 04 (0x04) Read Input Registers
This function reads back the 2 analogue inputs as registers 1-2
Registers 3-8 are always zero
Registers 9-24 are 16 registers representing 8 counter values. As modbus registers are 16-bits
wide and the counters are 32-bit, a counter is stored in 2 16-bit registers, high word first. In
the same way, the 16 registers 25-40 hold the 8 capture values.
Register 9 Counter1 high word
Register 10 Counter1 low word
Register 11 Counter2 high word
Register 12 Counter2 low word
Register 13 Counter3 high word
Register 14 Counter3 low word
Register 15 Counter4 high word
Register 16 Counter4 low word
Register 17 Counter5 high word
Register 18 Counter5 low word
Register 19 Counter6 high word
Register 20 Counter6 low word
Register 21 Counter7 high word
Register 22 Counter7 low word
Register 23 Counter8 high word
Register 24 Counter8 low word
Register 25 Capture1 high word
Register 26 Capture1 low word
Register 27 Capture2 high word
Register 28 Capture2 low word
Register 29 Capture3 high word
Register 30 Capture3 low word
Register 31 Capture4 high word
Register 32 Capture4 low word
Register 33 Capture5 high word
Register 34 Capture5 low word
Register 35 Capture6 high word
Register 36 Capture6 low word
Register 37 Capture7 high word
Register 38 Capture7 low word
Register 38 Capture8 high word
Register 40 Capture8 low word
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