User Manual
CANopen/PROFIBUS DP Gateway
GT200-DP-CO
WWW.SSTCOMM.COM
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The compression way mainly uses “SFC 15” when sending and receiving uses “SFC 14”:
4.3.4 How Step7 Select Data Module
Generally, when the data modules include “Consistent”, this means this data module is length integrity. When
accessing data, you need to use SFC14 (read) and SFC15 (write) to read or write data. And those which didn’t
include “Consistent”, you can use “Move” command to access the data.
According to user’s demand of input/output bytes, there are so many alternatives for the selection of data
modules. For example: When user needs 20-words input ( The data number reading form Modbus slave through
PLC is 20 words), user can directly select data modules no less than 20 words input (32words Input
、
64words
Input…) or input one input/output modules no less than 20 words (56 words Input
，
56words Output…).
Take “2 words Input Consistent” as an example, when you choose the module, you must use “SFC 14” to
access the data address. When some data of Modbus slave is two-word data, and needs high accuracy and real-
time, user generally select “2 words Input Consistent”, and not to select “2 words Input”. So, PLC can access the
whole data module during reading data, and it can also prevent data from burst changing (last word data and next
word data are not read in the same time) and causing incorrect data.
