MB89620 series
CHAPTER 8 PULSE WIDTH COUNT TIMER (PWC)
173
n
Measuring long pulse widths
To measure pulse widths longer than 2
8
times the cycle of the selected count clock, it is
necessary to either use an external circuit to count the number of inversions of the WTO pin
(PCR2: TO) or to count the number of counter underflows (01
H
→
00
H
) by software in the
interrupt processing routine. Counting by software requires a buffer in RAM (a software counter)
to hold the number of counter underflows (01
H
→
00
H
).
After initializing the software counter and enabling counter operation, the counter starts
counting-down from “FF
H
” when a measurement start edge is detected on the pulse input to the
PWC pin.
An interrupt request is generated on detection of the measurement completion edge or when
the counter underflows (01
H
→
00
H
). Check the measurement completion interrupt request flag
bit (PCR1: IR) and underflow (01
H
→
00
H
) interrupt request flag bit (PCR1: UF) in the interrupt
processing routine. If the UF bit is “1”, write “0” to the UF bit to clear the interrupt request and
increment the software counter (the PWC counter continues to operate).
When the IR bit is “1”, calculate the pulse width (including underflows (01
H
→
00
H
)) from the
values of the software counter and PWC reload buffer register (RLBR).
When the RLBR register value is “00
H
”, calculate as 256.
l
Calculating the width of long pulses
Pulse width = [(256 – RLBR register value) + (number of counter underflows (01H
→
00H)
×
256)]
×
one-cycle width of
count clock
Calculate the pulse width before the next underflow (01
H
→
00
H
) occurs. The correct
measurement value may not be able to be calculated after the next underflow (01
H
→
00
H
)
occurs.
Figure 8.6c shows the operation when the measured pulse selection bits (PCR2: W1, W0) are
set to “11
B
” (falling edge to falling edge).
Figure 8.6c Measuring Long Pulse Widths
Input pulse
(input waveform to the PWC pin)
EN bit
FF
H
Software
counter value
Counter value
UF bit
IR bit
BF bit
Set “0”
One cycle
Cleared by the program
Cleared by the program
Data transferred from down-counter
to RLBR
RLBR read
0
1
2
3
Содержание F2MC-8L MB89620 Series
Страница 8: ......
Страница 10: ...MB89620 series ...
Страница 11: ...vi MB89620 series ...
Страница 17: ...xii MB89620 series ...
Страница 18: ...xvi MB89620 series ...
Страница 30: ...MB89620 series CHAPTER 1 OVERVIEW 9 Memo ...
Страница 34: ...MB89620 series CHAPTER 1 OVERVIEW 13 Memo ...
Страница 42: ...MB89620 series CHAPTER 1 OVERVIEW 21 Memo ...
Страница 49: ...28 CHAPTER 1 OVERVIEW MB89620 series ...
Страница 62: ...MB89620 series CHAPTER 3 CPU 41 Memo ...
Страница 78: ...MB89620 series CHAPTER 3 CPU 57 Memo ...
Страница 82: ...MB89620 series CHAPTER 3 CPU 61 Memo ...
Страница 86: ...MB89620 series CHAPTER 3 CPU 65 Memo ...
Страница 90: ...MB89620 series CHAPTER 3 CPU 69 Memo ...
Страница 96: ...MB89620 series CHAPTER 3 CPU 75 Memo ...
Страница 122: ...MB89620 series CHAPTER 4 I O PORTS 101 Memo ...
Страница 144: ...MB89620 series CHAPTER 5 TIMEBASE TIMER 123 Memo ...
Страница 149: ...128 CHAPTER 5 TIMEBASE TIMER MB89620 series ...
Страница 157: ...136 CHAPTER 6 WATCHDOG TIMER MB89620 series ...
Страница 174: ...MB89620 series CHAPTER 7 8 BIT PWM TIMER 153 Memo ...
Страница 177: ...156 CHAPTER 7 8 BIT PWM TIMER MB89620 series ...
Страница 202: ...MB89620 series CHAPTER 9 16 BIT TIMER COUNTER 181 Memo ...
Страница 217: ...196 CHAPTER 9 16 BIT TIMER COUNTER MB89620 series ...
Страница 220: ...MB89620 series CHAPTER 10 8 BIT SERIAL I O SERIAL I O 1 AND SERIAL I O 2 199 Memo ...
Страница 228: ...MB89620 series CHAPTER 10 8 BIT SERIAL I O SERIAL I O 1 AND SERIAL I O 2 207 Memo ...
Страница 245: ...224 CHAPTER 10 8 BIT SERIAL I O SERIAL I O 1 AND SERIAL I O 2 MB89620 series ...
Страница 266: ...MB89620 series CHAPTER 13 A D CONVERTER 245 13 Memo ...
Страница 283: ...262 CHAPTER 13 A D CONVERTER MB89620 series ...
Страница 289: ...268 CHAPTER 14 CLOCK MONITOR FUNCTION MB89620 series ...
Страница 306: ...MB89620 series APPENDIX 285 APPEND Memo ...
Страница 319: ...298 APPENDIX MB89620 series Memo ...
Страница 321: ...2 ...
Страница 354: ......