Remote-processing CAMBASIC Manuel d'utilisateur télécharger pdf (Page 202)

Event Multitasking - 13

MULTITASKING ON A CLOCK TICK

The three 200 Hz (100 Hz in 9 MHz systems) tick timers are used for a number of multitasking functions in CAMBASIC.

In multitasking, it is used as a periodic interrupt. The ON T ICK statement can call a subroutine as often as 200 (100 in 9

MHz systems) times per second, or once ever y 327.67 seconds. The syntax is:

ON TICK number, time GOSUB line/label

On every multiple of the specified time, program execution branches to the subroutine at the line/label. Program

execution resumes when the RETUR N statement is reached in the subroutine.

A simple exam ple would be as follows:

10 ON TICK 0,1 GOSUB 50

20 PRINT "foreground"

30 FOR C=0 TO 1000:NEXT

40 GOTO 20

50 INC A%

60 PRINT A

70 RETURN

Line 10 tells CAMBASIC to interrupt every 1.00 seconds and branch to line 50.

Lines 20 through 40 represent a foreground program. It prints, does a short delay and prints again.

Line 50 increm ents a variable and r epresents the num ber of seconds.

In some applications m ultiple interr upts are r equired. T his can be done with the TICK statem ent. The only lim itation is

that the interrupt times must be multiples of each other. For exam ple, 1. 0 and 3.0 seconds would be acceptable, but 1.0

and 2. 7 seconds w ould not.

Below is a program that demonstrates clock interrupts every 1 and 5 seconds.

10 ON TICK 0,1 GOSUB 50

20 PRINT "foreground"

30 DELAY .25

40 GOTO 20

50 PRINT TAB(20);"tick";

60 INC A%:IF A%=5 THEN A%=0:GOSUB 70 ELSE PRINT:RETURN

70 PRINT " tock"

80 RETURN

Line 10 sets up an interrupt every 1.00 seconds

Lines 20 through 40 simulate your foreground program, as in the first example.

Line 50 prints “tick” every second

Line 60 increments a second counter. When it reaches 5, the counter is reset and "tock" is printed at

line 70.

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Remote-processing CAMBASIC Manuel d'utilisateur Page 202