Entec LBS-751 Manual de início rápido - Página 11

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Quick Start Guide

LBS-751 Control

03h

Read Holding Register Command

Use function code 03h to read holding register values containing "bit words" or analog data.

To determine data address, add 125 (decimal) to Setting location in the Modbus User-

Defined Assignment Map above.

Example 1:

Phase-A Current Demand (IAD) is available using the 03h function to

read address 133 (Mod_08 Setting location + 125 = 133).

Example 2:

AC Power Fail is available using the 03h function to read address 169 as

noted in the Status Bit table above. AC Power Fail can be determined from the state of bit 1

using polarity convention where Logic 1 = True Condition. The Scada master will typically

collect 16 bits (2 Bytes) from address 169. The desired bit location is determined counting

from Right to Left starting with Bit-0.

representing AC Power Fail. (1 = AC Power Fail True, 0 = False).

Bytes

03h Read request format from Master

1 byte

2 bytes

03h Successful response format from Slave

1 byte

n bytes

2 bytes

03h command will collect all data from the LBS-751 User-Defined Assignment Map with a

single poll (125 registers). In many systems this method will collect Binary and Analog

points with a single poll allowing more devices to communicate with the Scada master.

Large Scada systems utilize 03h to collect binary words versus using 02h to retrieve single

binary bits.

The second bit counting from the right is Bit-1

Field

Slave Address

Function Code (03h)

Starting register address

Number of registers read (n)

CRC‐16

Slave Address

Function Code (03h)

Bytes of data (n)

Data (2‐250 Bytes)

CRC‐16

APPENDIX 2