HT46R23 datasheet(12/42 Pages) HOLTEK

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HT46R23

Rev. 1.30

August 17, 2001

CLR WDT1 and CLR WDT2. Of these two types of instruc-

tion, only one can be active depending on the ROM code

option -²CLR WDT times selection option².Ifthe ²CLR

WDT² is selected (i.e. CLRWDT times equal one), any ex-

ecution of the CLR WDT instruction will clear the WDT. In

case ²CLR WDT1² and ²CLR WDT2² are chosen (i.e.

CLRWDT times equal two), these two instructions must be

executed to clear the WDT; otherwise, the WDT may reset

the chip because of time-out.

If the WDT time-out period is selected fs/212 (ROM code

option), the WDT time-out period ranges from

fs/212~fs/213, since the ²CLR WDT² or ²CLR WDT1² and

²CLR WDT2² instructions only clear the last two stages of

the WDT.

Power down operation - HALT

The HALT mode is initialized by the ²HALT² instruction

and results in the following...

The system oscillator will be turned off but the WDT

oscillator keeps running (if the WDT oscillator is se-

lected).

The contents of the on chip RAM and registers remain

unchanged.

WDT will be cleared and recounted again (if the WDT

clock is from the WDT oscillator).

All of the I/O ports maintain their original status.

The PD flag is set and the TO flag is cleared.

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 PD flags are ex-

amined, the reason for chip reset can be determined.

The PD flag is cleared by system power-up or executing

the ²CLR WDT² instruction and is set when executing

the ²HALT² instruction. The TO flag is set if the WDT

time-out occurs, and causes a wake-up that only resets

the PC and SP; the others keep 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 the ROM code option. Awakening from an I/O

port stimulus, the program will resume execution of the

next instruction. If it is awakening from an interrupt, two

sequences may happen. If the related interrupt is dis-

abled or the interrupt is enabled but the stack is full, the

program will resume execution at the next instruction. If

the interrupt is enabled and the stack is not full, the regu-

lar interrupt response takes place. If an interrupt request

flag is set to ²1² before entering the HALT mode, the

wake-up function of the related interrupt will be disabled.

Once a wake-up event occurs, it takes 1024 tSYS (sys-

tem clock period) to resume normal operation. In other

words, a dummy period will be inserted after wake-up. If

the wake-up results from an interrupt acknowledgment,

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.

Reset

There are three ways in which a reset can occur:

RES reset during normal operation

RES reset during HALT

WDT time-out reset during normal operation

The WDT time-out during HALT is different from other

chip reset conditions, since it can perform a ²warm re -

set² that resets only the PC and SP, leaving the other cir-

cuits in their original state. Some registers remain un-

changed during other reset conditions. Most registers

are reset to the ²initial condition² when the reset condi-

tions are met. By examining the PD and TO flags, the

program can distinguish between different ²chip resets².

t SS T

RE S

VD D

S S T T i m e - out

Ch i p Re s e t

Reset timing chart

V DD

RE S

Reset circuit

W a r m R es et

WD T

HA L T

Co l d

Re s e t

RE S

S y s t em R e s et

SS T

10- bi t R i ppl e

C ount e r

OS C 1

Reset configuration

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