Flintec MCS-64 ModbusOnEthernet - Manual (Page 6)

Page 6 Manual MSC-64: Modbus on Ethernet
1. I
NTRODUCTION
1.1. Identification and Scope
This document describes the system design for the Modbus on Ethernet (EGM 87.1) and up to
64 Load Cell Digitizing Modules (LDM88.x) using the Flintec backplane system. It describes the
functionality of the backplane, the protocol used on the backplane and the Modbus mapping used
to access the LDM88 modules via the EGM87 Gateway.
1.2. Purpose
The purpose of this document is to specify functionality and performance of the Gateway and the
Load Cell Digitizing Modules (LDM88) with the available firmware versions (standard 88.183,
filling 88.184, loss in weight 88.185).
2. S YSTEM D ESIGN
2.1 General
This software connects an Ethernet network to the local backplane modules. The Gateway
transports commands and responses from and to the Ethernet.
Ethernet
ADAPTOR
Ethernet
ADAPTOR
BACKPLANE
LDM and other IO
Up to 64 modules per backplane
Ethernet
Figure 1- ETHERNET Gateway in context
2.2 Backplane handling
The Gateway translates Modbus requests to local backplane requests and local backplane
responses to Modbus responses. The Modbus is currently fixed to port 502 using an UDP/IP
connection. Multiple register access through the Ethernet will produce multiple accesses on the
local backplane. The PLC response timeout must allow 3.125 ms for each register access
required.
However reading registers 2000 or 2004 will cache register 2060 also allowing the PLC to
acquire the corresponding qualifier to the weight values.