KROHNE OPTISONIC V6 Modbus - Manual (Page 9)

2011-07-19
OPTISONIC_V6_Modbus_6.doc 9/29
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ts 5.3 Function 03: READ HOLDING REGISTERS
Function 03 reads the contents of 1 to 125 contiguous holding registers in the slave.
The maximum number of registers at each request is limited to 125 16-bit registers: 125 integers, 62 long
integers, 62 floats, 31 doubles or 31 long longs.
Request
The request message specifies the starting register and the quantity of registers to be read. Registers are
addressed starting from zero. Registers 1-16 are addressed as 0-15.
Example
A request to read from slave device 17, registers 40108-40110 (decimal), or starting from 9CAC (hex):
Starting address Number of data items
Header
--
Slave
Address
11(h)
Function
03(h)
Hi
9C(h)
Low
AB(h)
Hi
00(h)
Low
03(h)
Error check
--
Trailer
--
Response:
Data Header
--
Slave
address
11(h)
Function
03(h)
Byte
count
06(h)
(Reg.
40108
Hi)
02(h)
(Reg.
40108
Low)
2B(h)
(Reg.
40109
Hi)
00(h)
(Reg.
40109
Low)
00(h)
(Reg.
40110
Hi)
00(h)
(Reg.
40110
Low)
64(h)
Error
check
--
Trailer
--
For each register the first byte contains the high order byte, the second the low order byte.
The contents of register 40108 are shown as the two byte values of 02 2B hex (555 decimal). The contents
of register 40109 is 00 00 hex (0 decimal) and of register 40110 is 00 64 hex (100 decimal).
If the request is not applicable, an exception response will be sent. See chapter 5.10 for exception
responses.
5.4 Function 04: READ INPUT REGISTERS
Function 04 performs a “read” operation, similar to function 03. The difference is that function 04 addresses
input registers (which are “read-only”), whereas function 03 addresses holding registers (which are
“read/write”).
5.5 Function 05: WRITE SINGLE COIL
Function 05 writes the status of a logical (Boolean or ON/OFF) variable.
This function is not used, as in this application Boolean variables are not used as individual entities. Boolean
variables are represented by means of specific bits packed in 32 bit data word (type “Long”).
5.6 Function 06: WRITE SINGLE HOLDING REGISTER
Function 06 presets a value into a single holding register.
When the address is a broadcast, all slaves will process the request.
Request
The request specifies the register reference to be written. Registers are addressed starting from zero.