Generic Parameters

Introduction

This topic describes the management and operations of the controllers’ communication functions using the READ_VAR function block as an example. (The PLCopen standard defines rules for function blocks.)

NOTE: These parameters are common to all PLCCommunication function blocks (except ADDM).

Graphical Representation

The parameters that are common to all function blocks in the PLCCommunication library are highlighted in this graphic:

Common Parameters

These parameters are shared by several function blocks in the PLCCommunication library:

Input	Type	Comment
`Execute`	BOOL	The function is executed on the rising edge of this input. NOTE: When `xExecute` is set to TRUE at the first task cycle in RUN after a cold or warm reset, the rising edge is not detected.
`Abort`	BOOL	Aborts the ongoing operation at the rising edge
`Addr`	ADDRESS	Address of the targeted external device (can be the output of the ADDM function block)
`Timeout`	WORD	Exchange timeout is a multiple of 100 ms (0 for infinite) NOTE: The Timeout time is fixed at ≅1 s for the HMI SCU and cannot be set for the Modbus communication function blocks.
NOTE: A function block operation may require several exchanges. The timeout applies to each exchange between the controller and the modem, so the global duration of the function block might be longer than the timeout.

Output	Type	Comment
`Done`	BOOL	`Done` is set to `TRUE` when the function is completed successfully.
`Busy`	BOOL	`Busy` is set to `TRUE` while the function is ongoing.
`Aborted`	BOOL	`Aborted` is set to `TRUE` when the function is aborted with the `Abort` input. When the function is aborted, `CommError` contains the code `Canceled - 16#02` (exchange stopped by a user request).
`Error`	BOOL	`Error` is set to `TRUE` when the function stops because of a detected error. When there is a detected error, `CommError` and `OperError` contain information about the detected error.
`CommError`	BYTE	`CommError` contains communication error codes.
`OperError`	DWORD	`OperError` contains operation error codes.

NOTE: As soon as the Busy output is reset to 0, one (and only one) of these 3 outputs is set to 1:

Done
Error
Aborted

Function blocks require a rising edge in order to be initiated. The function block needs to first see the Execute input as false in order to detect a subsequent rising edge.

WARNING
	UNINTENDED EQUIPMENT OPERATION Always make the first call to a function block with its `Execute` input set to `FALSE` so that it will detect a subsequent rising edge. Failure to follow these instructions can result in death, serious injury, or equipment damage.

Function Execution

The function starts at the rising edge of the Execute input. The Busy output is then set to TRUE. This figure shows the function block's behavior when the operation is automatically completed (with or without detected errors):

Note 1: The Done or Error bit is set to TRUE during a task cycle only if Execute has already been reset to FALSE when the operation ended.

Function Aborted

This figure shows the function being aborted by the application. The rising edge of the Abort input cancels the ongoing function. In such cases, the aborted output is set to 1 and CommError contains the code Canceled - 16#02 (exchange stopped by a user request):

Note 1: The Abort bit is set to TRUE during a task cycle only if Execute has already been reset to FALSE when the abort request occurred.