Function 04: Read Input Register - Siemens ATC5300 Manual

The ATC answer is the following:
01
Where:
01 = ATC address (Slave 01)
04 = Function requested by the master
04 = Number of bytes sent by the ATC
00 00 00 7C = Hex value of the battery voltage = 124 = 12.4 VDC
FA 65 = CRC checksum
1.6

Function 04: Read Input Register

The Modbus® function 04 allows to read one or more consecutive registers from the slave
memory. The address of each measure is given in the chapter "Data Library" of this manual.
As for Modbus® standard, the address in the query message must be decreased by one from
the effective address reported in the table. If the measure address is not included in the table
or the number of requested registers exceeds 60, the ATC will return an error code (see error
table).
Master query:
Slave address
Function
MSB address
LSB address
MSB register number
LSB register number
MSB CRC
LSB CRC
In the above example slave 08 is requested for 8 consecutive registers beginning with address
10h. Thus, registers from 10h to 17h will be returned. As usual, the message ends with the
CRC checksum.
Slave response:
Slave address
Function
Byte number
MSB register 10h
LSB register 10h
—
MSB register 17h
LSB register 17h
MSB CRC
LSB CRC
The response is always composed of the slave address, the function code requested by the
master and the contents of the requested registers. The answer ends with the CRC.
ATC5300
Modbus Communication Protocol, Edition 03/2011, A5E02469001-02
04 04 00
1.6 Function 04: Read Input Register
00 00
08h
04h
00h
0Fh
00h
08h
21h
57h
08h
04h
10h
00h
00h
—
00h
00h
5Eh
83h
General Information
7C 65
9