参数资料
型号: ST6228CN1
厂商: 意法半导体
英文描述: ER 3C 3#16S SKT RECP WALL
中文描述: 8位单片机与微控制器/ D转换器,自动重加载定时器,UART的秘书长办公室,安全复位和28引脚封装
文件页数: 24/84页
文件大小: 561K
代理商: ST6228CN1
24/84
24
ST62T28C/E28C
DIGITAL WATCHDOG
(Cont’d)
The Watchdog is associated with a Data space
register (Digital WatchDog Register, DWDR, loca-
tion 0D8h) which is described in greater detail in
Section 3.3.1 Digital Watchdog Register (DWDR).
This register is set to 0FEh on Reset: bit C is
cleared to “0”, which disables the Watchdog; the
timer downcounter bits, T0 to T5, and the SR bit
are allset to “1”, thus selectingthe longest Watch-
dog timerperiod. This time period can be set to the
user’s requirements by setting the appropriate val-
ue for bits T0 to T5 in the DWDR register. The SR
bit must be set to “1”, since it is this bit which gen-
erates the Reset signal when it changes to “0”;
clearing this bit would generate an immediate Re-
set.
It should be noted that the order of the bits in the
DWDR register is inverted with respect to the as-
sociated bits in the down counter: bit 7 of the
DWDR register corresponds, in fact, to T0 and bit
2 to T5. The user should bear in mind the fact that
these bits are inverted and shifted with respect to
the physical counter bits when writing to this regis-
ter. The relationship between the DWDR register
bits and the physical implementation of the Watch-
dog timer downcounter is illustrated in Figure 17.
Only the 6 most significant bits may be used to de-
fine the time period, since it is bit 6 which triggers
the Reset when it changes to “0”. This offers the
user a choice of 64 timed periods ranging from
3,072 to 196,608 clock cycles (with an oscillator
frequency of8MHz, this is equivalent to timer peri-
ods ranging from 384
μ
s to 24.576ms).
Figure 17. Watchdog Counter Control
W
D0
D1
D3
D4
D5
D6
D7
W
C
SR
T5
T4
T3
T2
T1
D2
T0
OSC
÷
12
RESET
VR02068A
÷
2
8
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