This application note illustrates the different functions of the Programmable Counter Array (PCA) which are available on the 83C51FA and 83C51FB. Included are
cookbook samples of code in typical applications to simplify the use of the PCA. Since all the examples are written in assembly language, it is assumed the reader is
familiar with ASM51. For further information on these products or ASM51 refer to the Embedded Controller Handbook (Vol. I).
CONTENTS PAGE
PCA OVERVIEW? 1
PCA TIMER/COUNTER? 1
COMPARE/CAPTURE MODULES? 3
CAPTURE MODE? 5
Measuring Pulse Widths? 5
Measuring Periods? 7
Measuring Frequencies? 7
Measuring Duty Cycles? 9
Measuring Phase Differences? 10
Reading the PCA Timer? 13
COMPARE MODE? 13
SOFTWARE TIMER? 13
HIGH SPEED OUTPUT? 15
WATCHDOG TIMER? 18
PULSE WIDTH MODULATOR? 19
CONCLUSION? 21
APPENDICES
A. Test Routines? A-1
B. Duty Cycle Calculation? B-1
C. Special Function Registers? C-1
FIGURES PAGE
1. PCA Timer/Counter and Compare/
Capture Modules? 1
2. PCA Interrupt? 4
3. PCA Capture Mode? 5
4. Measuring Pulse Width? 5
5. Measuring Period? 7
6. Measuring Frequency? 7
7. Measuring Duty Cycle? 9
8. Measuring Phase Differences? 10
9. Software Timer Mode? 13
10. High Speed Output Mode? 15
11. Watchdog Timer Mode? 18
12. PWM Mode? 19
13. CCAPnH Varies Duty Cycle? 20
LISTINGS PAGE
1. Measuring Pulse Widths? 6
2. Measuring Frequencies? 8
3. Measuring Duty Cycle? 9
4. Measuring Phase Differences? 11
5. Software Timer? 14
6. High Speed Output (Without
Interrupt)? 15
7. High Speed Output (With Interrupt)? 16
8. High Speed Output (Single Pulse)? 17
9. Watchdog Timer? 19
10. PWM? 21
TABLES PAGE
1. PCA Timer/Counter Inputs? 2
2. CMOD Values? 2
3. Compare/Capture Mode Values? 3
4. PWM Frequencies? 20