At a Glance

Management parameters are grouped together in the form of an array of four integers. The values contained in this array can be used to manage communication functions.

NOTE: In technical documentation, these management parameters are also called a management table or report.
NOTE: The first two words are managed by the system. You are responsible for managing the last two words.
NOTE: For M580 Hot Standby systems, make the following edits to the management parameters in the Data Editor:

  • Uncheck the Exchange On STBY attribute for each of the four management parameters.

  • Initialize the Length parameter each time the function is called.

  • Set the Timeout parameter accordingly to your application:

    • If the communication function is send through the CPU, the typical timeout value is 500 ms.

    • If the communication function is send through a NOC module, the typical timeout value is 2 s.

Structure

The following table describes the structure of the data in the communication management table:

 

Order of the Word

Most Significant Byte

Least Significant Byte

Data managed by the system

1

Exchange number

Activity bit: rank 0

Cancel bit: rank 1

Immediate acknowledge bit: rank 2

2

operation report

communication report

Data managed by the user

3

Timeout

4

Length

Activity Bit

This bit indicates the execution status of the communication function.

It is set to 1 when launched and returns to 0 when its execution is complete.

This is the first bit of the first element of the table.

Declaration: If the management table has been declared as follows:

Tab_Gest ARRAY [1..4] OF INT, the activity bit is the bit with the notation Tab_Gest[1].0.

NOTE: the notation previously used requires configuration of the project properties in such a way as to authorize the extraction of bits on integer types. If this is not the case Tab_Gest[1].0 cannot be accessed in this manner.

Cancel Bit

To cancel the communication function (for Modicon M340 and Modicon M580 PLCs only) set this bit to 1 and relaunch the EF. This is another way than using the CANCEL EF.

Declaration: If the management table has been declared as follows:

Tab_Gest ARRAY [1..4] OF INT, the cancel bit is the bit with the notation Tab_Gest[1].1.

Programming example in ST: cancelling a READ_VAR function

IF (%MW40.0) THEN

SET(%MW40.1);

READ_VAR(ADDM(’0.0.0.6’), ’%MW’, 100, 10, %MW40:4, %MW10:10);

END_IF;

%MW40 is the GEST parameter (management table).%MW40.0 corresponds to the activity bit of the READ_VAR function and is set to 1 when the communication function is active. If this bit is set to 1, the program sets the %MW40.1 bit, the function cancel bit, to 1. This stops communication of the READ_VAR function.

NOTE: When using the communication function cancel bit contained in the function exchange management word (%MW40 in this example), the function (READ_VAR in this example) must be called in order to activate the cancellation of the exchange.
NOTE: When using the communication function cancel bit, it is possible to cancel a communication from an animation table. This can be done by simply setting the function cancel bit to 1 (%MW40.1 in this example) and then start again the communication function.

Immediate Acknowledge Bit

Used only for the INPUT_CHAR EF, this bit forces an immediate execution of the EF. This feature is useful when working with NOM modules on remote drops (the connection is automatically closed by the CRP module if no answer of the CRA module arrives in the two minutes). The function INPUT_CHAR can indeed remain infinitely active in the NOM module waiting for characters coming on the serial connection. When this feature is activated, the NOM module immediately answers to the input character request even if no character is available (of course with receive characters length set to 0).

Declaration: If the management table has been declared as follows:

Tab_Gest ARRAY [1..4] OF INT, the immediate acknowledge bit is the bit with the notation Tab_Gest[1].2.

Exchange Number

When a communication function is sent, the system automatically allocates it a number, enabling the exchange to be identified.

This number can be used where necessary to stop the exchange in progress (using the CANCEL function).