參數(shù)資料
型號: P83CL882
廠商: NXP Semiconductors N.V.
英文描述: 80C51 Ultra Low Power ULP telephony controller
中文描述: 80C51的超低功耗無鉛汽油電話控制器
文件頁數(shù): 44/88頁
文件大小: 328K
代理商: P83CL882
2001 Jun 19
44
Philips Semiconductors
Product specification
80C51 Ultra Low Power (ULP) telephony controller
P83CL882
6.7.2
W
ATCHDOG
T
IMER
P
RESCALER
R
EGISTER
(WDTIM)
The WDTIM SFR is used to initialize the prescaler of the on-chip Watchdog Timer.
Table 55
Watchdog Timer Prescaler Register (SFR address A6H; reset value 0000 0000)
The expiration time (t
exp)
can be calculated as follows:
t
exp
prescaler factor
(
)
=
Where:
prescaler factor = the dividing factor from prescaler (PSC1 and PSC2); 1, 2, 4, 6, 8, 10, 12 and 16
WDTIM = the 8-bit value (0 to 255) in the Watchdog Timer Prescaler Register
WDCON = the 4-bit value (0 to 15) reloaded in the Watchdog Timer
clock period = the period of the signal applied to pin XTAL1.
From the t
exp
formulae it follows that the maximum expiration time is:
t
exp(max)
= 16
×
(2 + 64
×
256)
×
16
×
(16)
×
(clock period) = 67206016
×
(clock period)
and the minimum expiration time is:
t
exp(min)
= 1
×
66
×
16
×
(clock period) = 1056
×
(clock period)
6.7.3
E
XAMPLE SEQUENCE TO RELOAD THE
W
ATCHDOG
T
IMER
An example of the reload sequence for the Watchdog Timer:
MOV WDCON,#00H;Clear COND and LD bit
ORL WDCON,#80H;Positive edge WDCON.7, prepare condition
ORL WDCON,#01H;Positive edge WDCON.0, reload the timer
7
6
5
4
3
2
1
0
WDTIM.7
WDTIM.6
WDTIM.5
WDTIM.4
WDTIM.3
WDTIM.2
WDTIM.1
WDTIM.0
MGT298
WATCHDOG TIMER
WATCHDOG PRESCALER
(WDTIM)
fpsc
Fig.23 Clocking the Watchdog timer.
2
64
WDTIM
1
+
(
)
×
+
{
}
×
16
WDCON
1
+
(
)
×
×
clock period
(
)
×
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