GE Hydran 201i Instruction Manual page 250

J.3.1.3 Read Holding Registers (03h) / Read Input Registers (04h)
This function code is used by the master to read one or more consecutive data
registers (actual values or settings). Data registers are always 16-bit (two-byte) values
transmitted with the high-order byte first. The maximum number of registers that can
be read in a single packet is 125. Since some PLC implementations of Modbus only
support one of function codes 03h and 04h, in this case, either function code can be
used to read one or more consecutive data registers.
determines the type of data being read. Table J - 10 below shows the format of the
master and slave packets.
Note: This Section demonstrates how to build and understand a 03h or 04h Modbus
request/response exchange. To read or write Hydran 201Ti analog data values, please
refer to the subsequent Sections.
Function Code
Request Starting Address
Quantity of Registers
Function Code
Response Byte count
Register Value
Error Code
Error
Exception Code
Table J - 10: Format for Read Holding Registers (03h) / Read Input Registers (04h)
* N = Quantity of Registers
Table J-12 presents, as an example, the reading of multiple data registers with the
address range 108–110.
J.3.1.4 Write Multiple Registers (10h)
This function is used to write one or more registers. Up to 125 (7Dh) registers can be
written per request. The starting address must be specified, followed by the quantity to
write, the byte count of data to write, and the data.
This function code is used by the master to modify the contents of a one or more
consecutive setting registers. Setting registers are 16-bit (two -byte) values transmitted
with the high-order byte first. Table J-11 shows the format of the master and slave
packets.
Note: This Section shows how to build and understand a 10h Modbus
request/response exchange. To read or write Hydran 201Ti's analog data values,
please refer to the subsequent Sections.
Page 250
Hydran* 201i Instruction Manual
1 byte 03h
2 bytes 0000h to FFFFh
2 bytes 1 to 125 (7Dh)
1 byte 03h
1 byte 2 x N *
N x 2 bytes
1 byte 83h
1 byte 01 or 02 or 03 or 04 or 06
The data starting address
MA-033 Rev. 14.0, 12-Nov-18