Ioincyc.How to perform IO operations inside the cycle

Product : ISaGRAF V3

Date : 5-March-1996

File : Ioincyc.How to perform IO operations inside the cycle.htm

Subject : How to perform IO operations inside the ISaGRAF cycle?

Keywords: OPERATE - I/O update

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It is possible with ISaGRAF to perform fast I/O handling during the

cycle, if this is supported by the ISaGRAF I/O driver. The idea is

to use the OPERATE call to achieve a single input or output

operation. Just prepare such entries in OEM driver (in oem_call

entry of str_iovar):

1: Operate: immediate scan of an input channel:

- code = function identifier (ex: 'SCAN_NOW' defined word)

- argument = 0 (unused)

- return value = input value (casted to integer type)

2: Operate: immediate refresh of an output channel:

- code = function identifier (ex: 'UPDATE_NOW' defined word)

- argument = output value casted to integer type (*)

- return value = return check (OK / not OK)

(*) this cannot be applied to message variables.

This may lead to such a programming in the application:

(* Example: ST with OPERATE calls for immediate I/O handling *)

imm_value := Operate (MyInputVar, SCAN_NOW, 0);

If imm_value <> 0 Then

rc := Operate (MyOutputVar, UPDATE_NOW, imm_value);

rc := Operate (MyOutputAlrm, UPDATE_NOW, 1);

End_If;

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