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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)
Summary of Contents for F-ZTAT H8/3642A Series
Page 6: ...Rev 6 00 Sep 12 2006 page iv of xx ...
Page 8: ...Rev 6 00 Sep 12 2006 page vi of xx ...
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Page 124: ...Section 5 Power Down Modes Rev 6 00 Sep 12 2006 page 102 of 526 REJ09B0326 0600 ...
Page 188: ...Section 6 ROM Rev 6 00 Sep 12 2006 page 166 of 526 REJ09B0326 0600 ...
Page 190: ...Section 7 RAM Rev 6 00 Sep 12 2006 page 168 of 526 REJ09B0326 0600 ...
Page 298: ...Section 9 Timers Rev 6 00 Sep 12 2006 page 276 of 526 REJ09B0326 0600 ...
Page 378: ...Section 12 A D Converter Rev 6 00 Sep 12 2006 page 356 of 526 REJ09B0326 0600 ...
Page 446: ...Section 13 Electrical Characteristics Rev 6 00 Sep 12 2006 page 424 of 526 REJ09B0326 0600 ...