ht82m9aae Holtek Semiconductor Inc., ht82m9aae Datasheet - Page 12

• Manufacturer Part Number: ht82m9aae
• Description: Usb Mouse Encoder 8-bit Mcu With Eeprom
• Manufacturer: Holtek Semiconductor Inc.

If the device operates in a noisy environment, using the
on-chip 32kHz RC oscillator (WDT OSC) is strongly rec-
ommended, since the HALT will stop the system clock.
The WDT overflow under normal operation will initialize
a ²chip reset² and set the status bit ²TO². But in the
HALT mode, the overflow will initialize a ²warm reset²
and only the program counter and SP are reset to zero.
To clear the contents of the WDT (including the WDT
prescaler), three methods are adopted; external reset (a
low level to RES), software instruction and a ²HALT² in-
struction. The software instruction include ²CLR WDT²
and the other set - ²CLR WDT1² and ²CLR WDT2². Of
these two types of instruction, only one can be active de-
pending on the ROM code option - ²CLR WDT times se-
lection option². If the ²CLR WDT² is selected (i.e.
CLRWDT times is equal to one), any execution of the
²CLR WDT² instruction will clear the WDT. In the case
that ²CLR WDT² and ²CLR WDT² are chosen (i.e.
CLRWDT times is equal to two), these two instructions
must be executed to clear the WDT; otherwise, the WDT
may reset the chip as a result of time-out.
Power Down Operation - HALT
The HALT mode is initialized by the ²HALT² instruction
and results in the following:
·
·
·
Rev. 1.20
The system oscillator will be turned off but the WDT
oscillator remains running (if the WDT oscillator is se-
lected).
The contents of the on-chip RAM and registers remain
unchanged.
The WDT and WDT prescaler will be cleared and re-
counted again (if the WDT clock is from the WDT os-
cillator).
WS2
0
0
0
0
1
1
1
1
WS1
0
0
1
1
0
0
1
1
WDTS (09H) Register
WS0
0
1
0
1
0
1
0
1
Division Ratio
1:128
1:16
1:32
1:64
1:1
1:2
1:4
1:8
Watchdog Timer
12
·
·
The system can leave the HALT mode by means of an
external reset, an interrupt, an external falling edge sig-
nal on port A or a WDT overflow. An external reset
causes a device initialization and the WDT overflow per-
forms a ²warm reset². After the TO and PDF flags are
examined, the cause for chip reset can be determined.
The PDF flag is cleared by a system power-up or exe-
cuting the ²CLR WDT² instruction and is set when exe-
cuting the ²HALT² instruction. The TO flag is set if the
WDT time-out occurs, and causes a wake-up that only
resets the program counter and SP; the others remain in
their original status.
The port A wake-up and interrupt methods can be con-
sidered as a continuation of normal execution. Each bit
in port A can be independently selected to wake-up the
device by mask option. Awakening from an I/O port stim-
ulus, the program will resume execution of the next in-
struction. If it awakens from an interrupt, two sequence
may occur. If the related interrupt is disabled or the inter-
rupt is enabled but the stack is full, the program will re-
sume execution at the next instruction. If the interrupt is
enabled and the stack is not full, the regular interrupt re-
sponse takes place. If an interrupt request flag is set to
²1² before entering the HALT mode, the wake-up func-
tion of the related interrupt will be disabled. Once a
wake-up event occurs, it takes 1024 t
period) to resume normal operation. In other words, a
dummy period will be inserted after a wake-up. If the
wake-up results from an interrupt acknowledge signal,
the actual interrupt subroutine execution will be delayed
by one or more cycles. If the wake-up results in the next
instruction execution, this will be executed immediately
after the dummy period is finished.
To minimize power consumption, all the I/O pins should
be carefully managed before entering the HALT status.
All of the I/O ports remain in their original status.
The PDF flag is set and the TO flag is cleared.
HT82M9AEE/HT82M9AAE
SYS
August 13, 2007
(system clock