Denso BHT-200QW Spezifikationen PDF herunterladen (Seite 141)

100

101

Chapter 9. Event Polling and Error/Event Trapping

133

9.4 Event (of Keystroke) Trapping

[ 1 ] Overview

If any of the function keys previously specified for keystroke trapping is pressed, event

trapping makes the program cause an interrupt so as to transfer control from the current

program to the specified event-handling routine.

This trapping facility checks whether any of the function keys is pressed or not between every

execution of the statements.

[ 2 ] Programming for trapping keystrokes

To trap keystrokes, use both the ON KEY...GOSUB and KEY ON statements. The ON

KEY...GOSUB statement designates the key number of the function key to be trapped and

the event-handling routine (to which control is to be transferred if a specified function key is

pressed) in its label. The KEY ON statement activates the designated function key.

This trapping cannot take effect until both the ON KEY...GOSUB and KEY ON statements have

been executed.

The keystroke of an unspecified function key or any of the numerical keys cannot be trapped.

The following program sample will trap keystroke of magic keys M1 and M2 (these keys are

numbered 30 and 31, respectively).

sub1

sub2

ON KEY (30)GOSUB sub1

ON KEY (31)GOSUB sub2

KEY (30)ON

KEY (31)ON

(Main routine)

END

(Event-handling routine 1)

RETURN

(Event-handling routine 2)

RETURN

The RETURN statement in the event-handling routine will return control to the statement

immediately following that statement where the keyboard interrupt occurred.

Even if a function key is assigned a null string by the KEY statement, pressing the function key

will cause a keyboard interrupt when the KEY ON statement activates that function key.

1 2 ... 136 137 138 139 140 141 142 143 144 145 146 ... 586 587

Kommentare zu diesen Handbüchern

Keine Kommentare

Denso BHT-200QW Spezifikationen Seite 141

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Barcodeleser Denso BHT-200QW