Emerson Autochangeover Controllers AC8 Manual do Utilizador descarregar pdf (Página 11)

Revision B.33 2/25/2011

Liebert Monitoring Group – Development

Page 11 of 149

RTU Framing

The example below shows a typical Q/R from a SiteLink module. In common terms, the master device initiates a

query asking slave device 2 for holding registers starting at holding register 40051 (decimal 50) and including

next 2 Registers (3 total).

Query Sample

Slave

Address

Function

Code

Starting

―Hi Byte‖

Starting

―Lo Byte‖

Number of

Registers

―Hi Byte‖

Number of

Registers

―Lo Byte‖

CRC16

―Hi Byte‖

CRC16

―Lo Byte‖

Response Sample

Slave

Address

Function

Code

Count:

Bytes of

Data

40051 Data

Hi Lo

40052 Data

Hi Lo

40053 Data

Hi Lo

CRC16

―Hi Byte

CRC16

―Lo Byte‖

01 58

00 FA

00 54

Slave address 2 responds to Function Code 3 with 6 bytes of hexadecimal data and ends with CRC16 checksum.

40052 = FA (hex) = 250 (decimal)

40053 = 54 (hex) = 84 (decimal)

ASCII Framing:

Framing in ASCII transmission mode is accomplished by the use of the unique colon (:) to indicate the beginning of the

frame and a carriage return (CR) line feed (LF) to delineate the end of the frame. The line feed also serves as a

synchronizing character which indicates that the transmitting station is ready to receive an immediate reply.

ASCII Example

Frame

Start

Slave

Address

Function

Code

Data

Error

Check

End of

Frame

Ready for

Data

2 Char

16-bits

2 Char

16-bits

N x 4 Char

N x 16-bits

Char = Character: 1 Character = 7 data bits, 1 start bit, 1 or 2 stop bits and 1 parity bit (optional)

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 148 149

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