GMS81C1102 / GMS81C1202
21.3 Internal RC-Oscillated Watchdog Timer Mode
In the Internal RC-Oscillated Watchdog Timer mode, the
on-chip oscillator is stopped. But internal RC oscillation
circuit is oscillated in this mode. The on-chip RAM and
Control registers are held. The port pins out the values held
by their respective port data register, port direction regis-
ters.
chip RAM. External interrupts allow both on-chip RAM
and Control registers to retain their values.
If I-flag = 1, the normal interrupt response takes place. In
this case, if the bit WDTON of CKCTLR is set to “0” and
the bit WDTE of IENH is set to “1”, the device will exe-
cute the watchdog timer interrupt service routine.(Figure
21-5) However, if the bit WDTON of CKCTLR is set to
“1”, the device will generate the internal RESET signal
and execute the reset processing. (Figure 21-6)
The Internal RC-Oscillated Watchdog Timer mode is
activated by execution of STOP instruction after set-
ting the bit WAKEUP and RCWDT of CKCTLR to
“01”. (This register should be written by byte opera-
tion. If this register is set by bit manipulation instruc-
tion, for example “set1” or “clr1” instruction, it may be
undesired operation)
If I-flag = 0, the chip will resume execution starting with
the instruction following the STOP instruction. It will not
vector to interrupt service routine (refer to Figure 21-1).
When exit from Internal RC-Oscillated Watchdog Timer
mode by external interrupt, the oscillation stabilization
time is required for normal operation. Figure 21-5 shows
the timing diagram. When release the Internal RC-Oscil-
lated Watchdog Timer mode, the basic interval timer is ac-
tivated on wake-up. It is increased from 00H until FFH. The
count overflow is set to start normal operation. Therefore,
before STOP instruction, user must be set its relevant pres-
caler divide ratio to have long enough time (more than
20msec). This guarantees that oscillator has started and
stabilized.
Note: After STOP instruction, at least two or more NOP in-
struction should be written
Ex) LDM WDTR,#1111_1111B
LDM CKCTLR,#0010_1110B
LDM IRQH,#0
LDM IRQL,#0
STOP
NOP
NOP
By reset, exit from internal RC-Oscillated Watchdog Tim-
er mode is shown in Figure 21-6.
Release the Internal RC-Oscillated Watchdog Timer mode
The exit from Internal RC-Oscillated Watchdog Timer
mode is hardware reset or external interrupt. Reset re-de-
fines all the Control registers but does not change the on-
Oscillator
(X pin)
IN
Internal
RC Clock
Internal
Clock
External
Interrupt
(or WDT Interrupt)
Clear Basic Interval Timer
STOP Instruction Execution
BIT
Counter
N-1
N
N+1
N+2
N-2
00
01
FE FF 00
00
Normal Operation
Stabilization Time
ST > 20mS
RCWDT Mode
Normal Operation
t
Figure 21-5 Internal RCWDT Mode Releasing by External Interrupt or WDT Interrupt
66
Jan. 2002 ver 2.0
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