Table of Contents
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GE Consumer & Industrial
DESCRIPTION
INTERNAL MEMORY
BUFFER STRUCTURE
P485 MODBUS TO PROFIBUS CONVERTER – USER GUIDE
P485 Modbus to Profibus
Converter
Chapter 3: Data exchange
Data exchange
Overview
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.
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.
Internal Memory Buffer
Input data
(up to 244 bytes)
Output data
(up to 244 bytes)
1024 bytes
Figure 3-1: Internal memory buffer
3–1
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