Beckhoff BC7300 Bedienungsanleitung PDF herunterladen (Seite 20)

MODBUS

20 BC7300

Cable

BC7300

TxD/RxD (3)

RxD/TxD (8)

BC7300

RxD/TxD (3)

TxD/RxD (8)

Abschirmung

Sub-D socket

6: 5 V

5: GND

3: RxD/TxD

8: RxD/TxD

Bus termination

The MODBUS requires termination resistors at the beginning and end of

the bus lines.

RxD/TxD (3)

TxD/RxD (8)

GND (5)

5 V (6)

Process Data and Memory Map

The following example illustrates how the process image is constructed in

the Bus Terminal Controller, and the functions of the MODBUS telegram

with which digital and analog values can be read.

The Bus Terminal Controller has two process images. One is the fieldbus

interface and the other is the process image on the Bus Terminal

Controller. Bus Terminals can be assigned to one or the other process

image. The PLC variables offer an interface between these two process

images.

MODBUS

The input process image of the BC7300 starts from address 0x0000. All

the byte-oriented Bus Terminals (see Appendix) are entered here into the

process image first. The bit-oriented Bus Terminals them follow, and each

word (16 bit) is filled before starting a new one. The PLC variables are

entered into the process image last.

The output process image starts at address 0x0800. The entry begins

again here with the byte-oriented Bus Terminals, continues with the bit-

oriented Bus Terminals and finally the PLC variables.

All the digital signals can be directly addressed with functions 1, 2, 5 and

15.

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Beckhoff BC7300 Bedienungsanleitung Seite 20