Instructions
ECL Comfort 210 / 310, communication description
7.
Modbus protocol
The ECL 210/310 controllers are Modbus compliant devices.
The controller supports a number of public function codes.
The Modbus application data unit (ADU) is limited to 240
bytes.
Supported public function codes
03 (0x03) Read Holding Registers
04 (0x04) Read Input Registers
06 (0x06) Write Single Register
7.1
Function codes
Table 7-1: Function codes
Function Function
code Comments
Read PNU
0x03 or 0x04
Single PNU/register only
Write PNU
0x06
Single PNU/holding register only
7.1.1
Modbus messages
7.1.1.1
Read read-only parameter (0x03)
This function is used to read the value of an ECL Comfort
read-only parameter number. Values are always returned as
integer values and must be scaled according to the parameter
definition.
Requesting a quantity of more than 123 parameters in
sequence gives an error response. Requesting non-existing
parameter number(s) will give an error response.
Request
Function code
1 byte
0x03
Start PNU
2 bytes
0x0001 – 0xffff
Quantity N of PNU
2 bytes
0x0001 – 0x007B
Response
Function code
1 byte
0x03
Byte count
1 byte
2 – 246
PNU data value
2 bytes
0x0000 – 0xffff
Error
Function code
1 byte
0x83
Error code
2 bytes
1, 2, 3 or 4
The request/response is Modbus compliant when reading a
sequence of parameters (read input register).
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