Objects associated with specific applications
Explicit exchanges: General
Introduction Explicit exchanges are exchanges carried out on request of the program user using instructions: l l l l l
READ_STS (reading status words),
WRITE_CMD (writing command words),
WRITE_PARAM (writing adjustment parameters),
READ_PARAM (reading adjustment parameters),
SAVE_PARAM (saving adjustment parameters), l RESTORE_PARAM (restoring 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: terminal block fault, module absent…) and the additional orders for advanced programming of the application specific functions (for more information on the explicit exchange Objects which are relative to a task, you can refer to the corresponding chapter).
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
I/O module or interface built-in application
%MWy.i.r objects
or
%MWy.MOD.r (1)
Status words READ_STS
Status words
Command words
WRITE_CMD
Command words
Adjustment parameters: current
WRITE_PARAM
READ_PARAM
SAVE_PARAM
Adjustment parameters: current
Adjustment parameters: initial
RESTORE_PARAM
(1) Only with the instructions READ_STS and WRITE_CMD.
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TLX DS 37 PL7 xxE
Managing exchanges
Objects associated with specific applications
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 l the detection of an exchange which is in progress, the end of exchange report.
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
Logical channel
%CHy.i
The %CHy.i channel is a general syntax for updating all of the objects which are of the same type and linked to this channel or to this group of channels, via the explicit instructions.
Example: READ_STS%CH2.3
(reading the status words of channel 3 on module 2).
Note: In the case of a group of channels, the address used has to be the address of the first channel in the group of channels which is managed by the module.
Example: In the case of 32 discrete inputs (4 groups of 8 input channels, 0 to 7, 8 to 15, …) situated in slot 3. In order to read channel 12’s status words (fifth channel of the second group of channels), the syntax to use is: READ_STS%CH3.8
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TLX DS 37 PL7 xxE
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