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P485 MODBUS TO PROFIBUS CONVERTER – USER GUIDE 3–1

GE Consumer & Industrial

P485 Modbus to Profibus

Converter

Chapter 3: Data exchange

Data ex change

Overview

DESCRIPTION Data from the fieldbus (Profibus) and the sub network (Modbus) is stored in an internal

memory buffer. This is a easy method for data exchange where the fieldbus control

system simply reads and writes data to pre-defined memory locations, and the serial sub

network also use the same internal memory buffer to read and write data. Refer to Figure

3-2: Data exchange overview on page 3–2 for details.

INTERNAL MEMORY

BUFFER STRUCTURE

The internal memory buffer can be seen as a memory space with three different types of

data; input data, output data and general data.

• Input data: This is data that should be sent to the fieldbus. The P485 can handle up to

244 bytes of input data. The total input/output data must not exceed 416 bytes.

• Output data: this is data recieved from the fieldbus. The P485 can handle up to 244

bytes of output data.

• General data: This data cannot be accessed from the fieldbus, and is used for

transfers between nodes on the sub-network, or as a general “scratch pad” for data.

The P485 can handle up to 1024 bytes of general data.

Figure 3-1: Internal memory buffer

Internal Memory Buffer

Output data

(up to 244 bytes)

Input data

(up to 244 bytes)

Sub Network

Fieldbus

General data

1024 bytes

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Ge P485 Manuel d'utilisateur Page 19