MC95FG0128A
80
Aug 02, 2018 Ver.2.9
11.3 WDT
11.3.1 Overview
The watchdog timer rapidly detects the CPU malfunction such as endless looping caused by noise or
the like, and resumes the CPU to the normal state. The watchdog timer signal for detecting
malfunction can be selected either a reset CPU or an interrupt request. When the watchdog timer is
not being used for malfunction detection, it can be used as a timer to generate an interrupt at fixed
intervals. It is possible to use free running 8-bit timer mode (WDTRSON=
’0’) or watch dog timer mode
(WDTRSON=
’1’) as setting WDTMR[6] bit. If writing WDTMR[5] to ‘1’, WDT counter value is cleared
and counts up. After 1 machine cycle, this bit has
‘0’ automatically. The watchdog timer consists of 8-
bit binary counter and the watchdog timer data register. When the value of 8-bit binary counter is
equal to the 8 bits of WDTR, the interrupt request flag is generated. This can be used as Watchdog
timer interrupt or reset the CPU in accordance with the bit WDTRSON.
The clock source of Watch Dog Timer is BIT overflow output. The interval of watchdog timer interrupt
is decided by BIT overflow period and WDTR set value. The equation is as below
WDT Interrupt Interval = (BIT Interrupt Interval) X (WDTR Value+1)
11.3.2 Block Diagram
Figure 11.3 WDT Block Diagram
11.3.3 Register Map
Table 11-4 Register Map
Name
Address
Dir
Default
Description
WDTR
8EH
W
FFH
Watch Dog Timer Register
WDTCR
8EH
R
00H
Watch Dog Timer Counter Register
WDTMR
8DH
R/W
00H
Watch Dog Timer Mode Register
To Reset
Circuit
[8E
H
]
Clear
WDTEN
BIT Overflow
WDTCR
WDTR
Watchdog Timer
Register
[8E
H
]
Watchdog Timer
Counter Register
WDTIFR
WDTMR
WDTCL
WDTRSON
INT_ACK
Clear
WDTIF
Summary of Contents for MC95FG0128A
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