HT45RM03 datasheet(13/54 Pages) HOLTEK

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HT45RM03

Rev. 1.10

February 16, 2007

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

· The PDF 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 signal

on port A or a WDT overflow. An external reset causes a

device initialization and the WDT overflow performs a

²warm reset². After the TO and PDF flags are examined,

the reason for chip reset can be determined. The PDF

flag is cleared by system power-up or executing the

²CLR

WDT

² 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 program

counter 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 options. Awakening from an I/O port stim-

ulus, the program will resume execution of the next in-

struction. 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 -

set

² that resets only the program counter and SP, leav-

ing the other circuits in their original state. Some regis-

ters remain unchanged during other reset conditions.

Most registers are reset to the

²initial condition² when

the reset conditions are met. By examining the PDF and

TO flags, the program can distinguish between different

²chip resets².

PDF

RESET Conditions

RES reset during power-up

RES reset during normal operation

RES wake-up HALT

WDT time-out during normal operation

WDT wake-up HALT

Note:

²u² means ²unchanged²

To guarantee that the system oscillator is started and

stabilized, the SST (System Start-up Timer) provides an

extra-delay of 1024 system clock pulses when the sys-

tem reset (power-up, WDT time-out or RES reset) or the

system awakes from the HALT state.

When a system reset occurs, the SST delay is added

during the reset period. Any wake-up from HALT will en-

able the SST delay. The functional unit chip reset status

are shown below.

W a r m R e s e t

W D T

H A L T

C o l d

R e s e t

R E S

S y s t e m R e s e t

S S T

1 0 - b i t R i p p l e

C o u n t e r

O S C 1

Reset Configuration

t S S T

R E S

V D D

S S T T i m e - o u t

C h i p R e s e t

Reset Timing Chart

R E S

V D D

1 0 0 k W

1 0 k W

0 . 1 m F *

0 . 0 1 m F *

Reset Circuit

Note:

²*² Make the length of the wiring, which is con-

nected to the RES pin as short as possible, to

avoid noise interference.

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