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Chromalox Instruments and Controls

A-51643 Rev. 6 10/06/03 41

Query

Field Name

RTU Example Data

Description

Header

> 3.5 idle characters

Start characters

Slave Address

$06

Slave number 6

Function

$03

Read multiple registers

Starting Address Hi

$00

Start reading at holding register 108

Starting Address Lo

$6B

No. of Registers Hi

$00

Read 3 successive holding registers

No. of Registers Lo

$03

CRC Lo

$75

CRC = $A075

CRC Hi

$A0

Trailer

> 3.5 idle characters

End characters

Response

Field Name

RTU Example Data

Description

Header

> 3.5 idle characters

Start characters

Slave Address

$06

Slave number 6

Function

$03

Read multiple registers

Byte Count

$06

Number of data bytes to follow

Data Hi

$02

Contents of holding register 108

Data Lo

$2B

Data Hi

$00

Contents of holding register 109

Data Lo

$00

Data Hi

$00

Contents of holding register 110

Data Lo

$62

CRC Lo

$88

CRC = $8862

CRC Hi

$49

Trailer

> 3.5 idle characters

End characters

6.7.1 The Byte Count Field

When constructing responses in buffers, use a Byte Count value that equals the count of 8-bit bytes in

your message data. The value is exclusive of all other field contents, including the Byte Count field.

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