HT47C20 Holtek Semiconductor Inc, HT47C20 Datasheet - Page 19

• Manufacturer Part Number: HT47C20
• Description: 8-Bit Microcontroller
• Manufacturer: Holtek Semiconductor Inc

Once a wake-up event occurs, it takes 1024 t
(system clock period) to resume normal opera-
tion. In other words, a dummy period will be in-
serted after the wake-up. If the wake-up results
from an interrupt acknowledgment, the actual
interrupt subroutine execution is delayed by
one more cycle. If the wake-up results in the
next instruction execution, this will execute im-
mediately after a dummy period has finished.
To minimize power consumption, all the I/O
pins should be carefully managed before enter-
ing the HALT status.
Reset
·
·
·
·
The WDT time-out during HALT is different
from other chip reset conditions, since it can
perform a warm reset that just resets the PC
and SP leaving the other circuits in their origi-
nal state. Some registers remain unchanged
during any other reset conditions. Most regis-
ters are reset to the ²initial condition² when the
reset conditions are met. By examining the PD
and TO flags, the program can distinguish be-
tween different ²chip resets².
Note: ²u² means ²unchanged².
Therearethreewaysinwhicharesetmayoccur.
RES reset during normal operation
RES reset during HALT
WDT time-out reset during normal operation
TO
0
u
0
1
1
PD
0
u
1
u
1
RES reset during power-up
RES reset during normal
operation
RES wake-up HALT
WDT time-out during normal
operation
WDT wake-up HALT
RESET Conditions
SYS
19
To guarantee that the system oscillator has
started and stabilized, the SST (System
Start-up Timer) provides an extra delay. There
is an extra delay of 1024 system clock pulses
when the system awakes from the HALT state
or when the system powers up.
The functional unit chip reset status are shown
below.
PC
Interrupt
Prescaler, Divider
WDT, RTC, Time
Base
Timer/event counter Off
Input/output ports
SP
Reset timing chart
000H
Disabled
Cleared
Clear. After master
reset, begin counting
Input mode
Points to the top of
the stack
January 18, 2000
HT47C20