参数资料
型号: ST62P18CB1/XXX
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PDIP20
封装: 0.300 INCH, PLASTIC, DIP-20
文件页数: 18/82页
文件大小: 937K
代理商: ST62P18CB1/XXX
Obsolete
Product(s)
- Obsolete
Product(s)
25/82
ST62T18C/E18C
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 all set to “1”, thus selecting the longest Watch-
dog timer period. 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 of 8MHz, this is equivalent to timer peri-
ods ranging from 384 s to 24.576ms).
Figure 17. Watchdog Counter Control
W
A
T
CHDO
G
CO
NT
RO
L
RE
G
IS
T
E
R
D0
D1
D3
D4
D5
D6
D7
WA
T
CHDO
G
CO
UNT
E
R
C
SR
T5
T4
T3
T2
T1
D2
T0
OSC
÷12
RESET
VR02068A
÷28
25
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