参数资料
型号: ST72E331N4D0
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, UVPROM, 8 MHz, MICROCONTROLLER, CDIP56
封装: 0.600 INCH, WINDOWED, CERAMIC, SDIP-56
文件页数: 40/107页
文件大小: 691K
代理商: ST72E331N4D0
38/107
ST72E331 ST72T331
WATCHDOG TIMER (Cont’d)
The application program must write in the CR reg-
ister at regular intervals during normal operation to
prevent an MCU reset. The value to be stored in
the CR register must be between FFh and C0h
(see Table 1):
– The WDGA bit is set (watchdog enabled)
– The T6 bit is set to prevent generating an imme-
diate reset
– The T[5:0] bits contain the number of increments
which represents the time delay before the
watchdog produces a reset.
Table 13.Watchdog Timing (fCPU = 8 MHz)
Notes: Following a reset, the watchdog is disa-
bled. Once activated it cannot be disabled, except
by a reset.
The T6 bit can be used to generate a software re-
set (the WDGA bit is set and the T6 bit is cleared).
If the watchdog is activated, the HALT instruction
will generate a Reset.
5.3.4 Hardware Watchdog Option
If Hardware Watchdog is selected by option byte,
the watchdog is always active and the WDGA bit in
the CR is not used.
Refer to the device-specific Option Byte descrip-
tion.
5.3.5 Low Power Modes
5.3.6 Interrupts
None.
5.3.7 Register Description
CONTROL REGISTER (CR)
Read/Write
Reset Value: 0111 1111 (7Fh)
Bit 7 = WDGA
Activation bit.
This bit is set by software and only cleared by
hardware after a reset. When WDGA = 1, the
watchdog can generate a reset.
0: Watchdog disabled
1: Watchdog enabled
Note: This bit is not used if the hardware watch-
dog option is enabled by option byte.
Bit 6:0 = T[6:0]
7-bit timer (MSB to LSB).
These bits contain the decremented value. A reset
is produced when it rolls over from 40h to 3Fh (T6
becomes cleared).
STATUS REGISTER (SR)
Read/Write
Reset Value*: 0000 0000 (00h)
Bit 0 = WDOGF
Watchdog flag.
This bit is set by a watchdog reset and cleared by
software or a power on/off reset. This bit is useful
for distinguishing power/on off or external reset
and watchdog reset.
0: No Watchdog reset occurred
1: Watchdog reset occurred
* Only by software and power on/off reset
Note: This register is not used in versions without
LVD Reset.
CR Register
initial value
WDG timeout period
(ms)
Max
FFh
98.304
Min
C0h
1.536
Mode
Description
WAIT
No effect on Watchdog.
HALT
Immediate reset generation as soon as
the HALT instruction is executed if the
Watchdog is activated (WDGA bit is
set).
70
WDGA
T6
T5
T4
T3
T2
T1
T0
70
-
WDOGF
38
相关PDF资料
PDF描述
ST72T331N2B6S 8-BIT, OTPROM, 8 MHz, MICROCONTROLLER, PDIP56
ST72T331J2T3S 8-BIT, OTPROM, 4 MHz, MICROCONTROLLER, PQFP44
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