Prosoft-technology MVI69L-MBS Manuale Utente Scaricare il pdf (Pagina 110)

Reference MVI69L-MBS ♦ CompactLogix Platform

User Manual Communication Module

Page 110 of 154 ProSoft Technology, Inc.

January 6, 2014

Node

Address

Function

Code

Data Start

Point High

Data Start

Point Low

Number of

Points High

Number of

Points Low

Error Check Field

(2 bytes)

CRC

Response

The addressed Slave responds with its address and the function code, followed

by the information field. The information field contains 1 byte describing the

quantity of data bytes to be returned. The contents of the registers requested

(DATA) are two bytes each, with the binary content right justified within each pair

of characters. The first byte includes the high order bits and the second, the low

order bits.

Because the Slave interface device is normally serviced at the end of the

controller's scan, the data reflects the register content at the end of the scan.

Some Slaves limit the quantity of register content provided each scan; thus for

large register quantities, multiple transmissions are made using register content

from sequential scans.

In the example below, the registers 40108 to 40110 have the decimal contents

555, 0, and 100 respectively.

Node

Address

Function

Code

Byte

Count

Data

Error Check Field

(2 bytes)

CRC

7.2.5 Read Input Registers (Function Code 04)

Query

This Function Code obtains the contents of the controller's input registers from

the Modbus 3x range. These locations receive their values from devices

connected to the I/O structure and can only be referenced, not altered from within

the controller, The addressing allows up to 125 registers to be obtained at each

request; however, the specific Slave device may have restrictions that lower this

maximum quantity. The registers are numbered for zero (30001 = zero, 30002 =

one, and so on). Broadcast mode is not allowed.

The example below requests the contents of register 30009 in Slave number 11.

Node

Address

Function

Code

Data Start

Point High

Data Start

Point Low

Number of

Points High

Number of

Points Low

Error Check

Field (2 bytes)

CRC

1 2 ... 105 106 107 108 109 110 111 112 113 114 115 ... 153 154

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