GMS81C2020 Datasheet, PDF (79/92 Pages) Hynix Semiconductor – CMOS Single-Chip 8-Bit Microcontroller with A/D Converter & VFD Driver

Hyundai Micro Electronics
GMS81C2020/GMS81C2120
Figure 21-6 Wake-up Timer Mode Releasing by External Interrupt or Timer0 Interrupt
21.4 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.
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 operea-
tion. If this register is set by bit manipulation instruc-
tion, for example "set1" or "clr1" instruction, it may
be undesired operation )
Note: Caution : After STOP instruction, at least two or
more NOP instruction should be written
Ex)
LDM WDTR,#1111_1111B
LDM CKCTLR,#0010_1110B
STOP
NOP
NOP
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 execute
the watchdog timer interrupt service routine.(Figure 21-7 )
However, if the bit WDTON of CKCTLR is set to "1", the
device will generate the internal RESET signal and exe-
cute the reset processing. (Figure 21-8 )
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 to normal operation. Figure 21-7 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 00_H until FF_H .
The count overflow is set to start normal operation. There-
fore, before STOP instruction, user must be set its relevant
prescaler divide ratio to have long enough time (more than
20msec). This guarantees that oscillator has started and
stabilized.
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-
chip RAM. External interrupts allow both on-chip RAM
and Control registers to retain their values.
By reset, exit from internal RC-Oscillated Watchdog Tim-
er mode is shown in Figure 21-8 .
Oscillator
(XI pin)
Internal
RC Clock
Internal
Clock
External
Interrupt
( or WDT Interrupt )
STOP Instruction Execution
BIT
Counter
N-2 N-1 N N+1
Normal Operation
N+2
RCWDT Mode
Clear Basic Interval Timer
00 01
FE FF 00 00
Stabilization Time
t_ST > 20mS
Normal Operation
Figure 21-7 Internal RCWDT Mode Releasing by External Interrupt or WDT Interrupt
Nov. 1999 Ver 0.0
preliminary
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