Emerson OpenComms-485 Bedienungsanleitung PDF herunterladen (Seite 7)

Modbus Communications

3

1.6 RTU Framing

The example below shows a typical query and response from a Liebert IntelliSlot 485 interface card.

The master device initiates a query asking Slave Device, with address 2, for holding registers

starting at holding register 40051 (offset 50) and including next 2 registers (3 total).

Table 4 Query sample

Starting Register Number of Registers CRC16 CRC16

Slave

Address

Function

Code

Hi Byte Lo Byte Hi Byte Lo Byte Hi Byte Lo Byte

02 03 00 32 00 03 E5 FA

Table 5 Response sample

Register CRC16

40051 Data 40052 Data 40053 Data

Slave

Address

Function

Code

Count:

Bytes of

Data

Hi Lo Hi Lo Hi Lo

Hi Byte Lo Byte

02 03 6 1 58 00 FA 00 54 1B 0D

Slave Device, with address 2, responds to Function Code 3 with 6 bytes of hexadecimal data and

ends with CRC16 checksum.

Register values: 40051 = 158(hex) = 344 (decimal)

40052 = FA (hex) = 250 (decimal)

40053 = 54 (hex) = 84 (decimal)

1 2 3 4 5 6 7 8 9 10 11 12 ... 51 52

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