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Section 9 Timers
Rev. 6.00 Sep 12, 2006 page 274 of 526
REJ09B0326-0600
9.6.3 Timer
Operation
The watchdog timer has an 8-bit counter (TCW) that is incremented by clock input (
φ
/8192).
When TCSRWE = 1 in TCSRW, if 0 is written in B2WI and 1 is simultaneously written in
WDON, TCW starts counting up (two write accesses to TCSRW are necessary in order to operate
the watchdog timer). When the TCW count value reaches H'FF, the next clock input causes the
watchdog timer to overflow and generates an internal reset signal. The internal reset signal is
output for 512 clock cycles of the
φ
OSC
clock. It is possible to write to TCW, causing TCW to
count up from the written value. The overflow period can be set in the range from 1 to 256 input
clocks, depending on the value written in TCW.
Figure 9.36 shows an example of watchdog timer operations.
Example:
φ
= 4 MHz and the desired overflow period is 30 ms.
4
×
10
6
8192
×
30
×
10
–3
= 14.6
The value set in TCW should therefore be 256 – 15 = 241 (H'F1).
H'F1
TCW overflow
Start
H'F1 written
in TCW
H'F1 written in TCW
Reset
Internal reset
signal
512
φ
OSC
clock cycles
H'FF
H'00
TCW count
value
Figure 9.36 Typical Watchdog Timer Operations (Example)
Содержание F-ZTAT H8/3642A Series
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Страница 21: ...Rev 6 00 Sep 12 2006 page xix of xx Appendix E Product Code Lineup 522 Appendix F Package Dimensions 524 ...
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Страница 124: ...Section 5 Power Down Modes Rev 6 00 Sep 12 2006 page 102 of 526 REJ09B0326 0600 ...
Страница 188: ...Section 6 ROM Rev 6 00 Sep 12 2006 page 166 of 526 REJ09B0326 0600 ...
Страница 190: ...Section 7 RAM Rev 6 00 Sep 12 2006 page 168 of 526 REJ09B0326 0600 ...
Страница 298: ...Section 9 Timers Rev 6 00 Sep 12 2006 page 276 of 526 REJ09B0326 0600 ...
Страница 378: ...Section 12 A D Converter Rev 6 00 Sep 12 2006 page 356 of 526 REJ09B0326 0600 ...
Страница 446: ...Section 13 Electrical Characteristics Rev 6 00 Sep 12 2006 page 424 of 526 REJ09B0326 0600 ...