Motorola Axiom CMD11E1 Betriebsanweisung PDF herunterladen (Seite 90)

90 CHAPTER 8. SIGNAL GENERATION

REST

ADDD TOC2

STD TOC2 ; BUMP ALARM SETTING

; TURN OFF THE FLAG!

LDAA #%01000000

STAA TFLG1

RTI

; Connect the service to the interrupt ;

ORG $00DC ; $00DC WHERE THE SERVICE STARTS

JMP SERVICE ; JUMP TO WHERE THE SERVICE CODE ACTUALLY IS

Assemble and run the above program. Connect PA4 to an oscilloscope and verify

that the duty cycle and the frequency are correct.

8.5 Variable frequency generator

We now modify the above code to create a variable frequency generator. The

program will monitor the keyboard and depending on the number the user enters,

it will change the frequency as shown in the table below:

Number Frequency Period Period On time Oﬀ time

seconds ticks ticks ticks

0 440 0.002273 4545 1136 3409

1 466 0.002145 4290 1073 3217

2 494 0.002025 4050 1013 3037

3 523 0.001911 3822 956 2866

4 554 0.001804 3608 902 2706

5 587 0.001703 3405 851 2554

6 622 0.001607 3214 804 2410

7 659 0.001517 3034 759 2275

8 698 0.001432 2863 716 2147

9 740 0.001351 2703 676 2027

As a programmer we are only interested in the on-time and oﬀ-time. We use FDB

to create two tables in the data section as shown below:

ONTIMETBL

FDB 1136 ,1073, 1013, 956, 902

1 2 ... 85 86 87 88 89 90 91 92 93 94 95 ... 100 101

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Motorola Axiom CMD11E1 Betriebsanweisung Seite 90