Language objects
Introduction to explicit exchanges
At a Glance Explicit exchanges are exchanges carried out on request of the program user using instructions: l l l l l l
READ_STS (reading of status words),
WRITE_CMD (writing of command words)
WRITE_PARAM (writing of adjustment parameters),
READ_PARAM (reading of adjustment parameters),
SAVE_PARAM (saving of adjustment parameters),
RESTORE_PARAM (restoring of adjustment parameters),
These exchanges apply to a group of %MW objects that are of the same type (status, command or parameter) on the same channel.
Note: These objects are not essential when programming a application-specific function, but they carry extra information (eg: Type of channel fault…), and supplementary commands (e.g.: positioning and adjustment commands) for more specialized programming of the application.
General principles on the use of the explicit instructions
The diagram below presents the different kinds of explicit exchanges that are possible between the PLC’s processor and the module (or the built-in interface).
PLC processor Application or interface module built-in application
%MWxy.i.r objects
or
%MWxy.MOD.r (1)
Status parameters
READ_STS
Status parameters
Command parameters
WRITE_CMD
Command parameters
Adjustment parameters current
WRITE_PARAM
READ_PARAM
SAVE_PARAM
Adjustment parameters current
Initial adjustment parameters
RESTORE_PARAM
(1) Only with the instructions READ_STS and WRITE_CMD.
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Management of the exchanges
Language objects
During an explicit exchange, it may be interesting to monitor the progress that this makes, in order, for example, not to take into consideration the data read until the exchange has been carried out successfully.
For this, two kinds of information are available: l detecting an exchange in progress (See Explicit exchange operation indicators: l
%MWxy.i.0, p. 182),
an end of exchange report (See
Explicit exchange report: %MWxy.i.1, p. 182).
The diagram below describes the principal of the management of an exchange
Execution of an explicit exchange
Detection of an exchange in progress
Report of the end of the exchange
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