KROHNE ALTOSONIC V12 EN - Manual (Page 117)

MODBUS PROTOCOL DESCRIPTION AND SET-UP
10
117
ALTOSONIC V12
www.krohne.com 04/2013 - 4002643502 - MA ALTOSONIC V12 R02 en
10.5.3 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):
Response
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.
For more information, refer to
Exception responses on page 120.
10.5.4 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").
Header Slave
address Function Starting address Number of data items Error
check
Trailer
-- 11(h) 03(h) Hi
9C(h)
Low
AB(h)
Hi
00(h)
Low
03(h)
-- --
Table 10-2: Example read holding registers
Header Slave
addres
s
Funct. Byte
count Data Error
check Trailer
-- 11(h) 03(h) 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)
-- --
Table 10-3: Response read holding registers