Eaton easyE4 Manual page 641

10.2.2.4 Read Input Registers 0x04:
Function 0x04 reads the analog inputs' registers word by word.
The Modbus client treats two bytes as one input register.
This means that in order to read an analog input with 32 bits, two consecutive input
registers must be read.
Table 117: Request-PDU
Function Code
Start address
Number of input registers
Response to the request being received
1. The starting address is analyzed (distributed among bytes 1 and 2)
b. Byte 1 = Hi; Byte 2 = Lo
2. The number of registers is analyzed (distributed among bytes 3 and 4)
b. Byte 3 = Hi; Byte 4 = Lo
3. The input registers are read from the start of the (starting address) to (starting
address + number of input registers)
(An input register corresponds to two bytes)
Table 118: Response-PDU
Function Code
Bye Count
Register values
n= Number of input registers read
Preparation for sending the response
1. The input registers read are mapped to two bytes per input register
2. There are a high byte and a low byte for each input register
a. The first byte = Hi; the second byte = Lo
b. Example:
- Register word Hi0x00
- Register word Lo0x0A
- Content of marker word 0x000A
3. The LSB within the byte is bit 0
Once the response is encoded, it is sent.
easyE4 10/19 MN050009 EN www.eaton.com
10. Connection to other devices
1 byte 0x04 ;Read Input Registers
2 byte Must always be 1 less than the starting input you
want (zero-based)
2 byte 1 to 125 (0x7D)
1 byte 0x04 ;Read Input Registers
1 byte A value of
= 2 * N must always be entered here
n* 2 byte Value
10.2 Modbus TCP
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