HT46R52A Просмотр технического описания (PDF) - Holtek Semiconductor

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HT46R52A

A/D Type 8-Bit OTP MCU

Holtek Semiconductor 

HT46R51A/HT46R52A

C L R W D T 1 F la g

C L R W D T 2 F la g

1 o r 2 In s tr u c tio n s

C o n tro l

L o g ic

fS Y S /4

W D T O s c illa to r

W D T S o u rc e

C o n fig u r a tio n

fS 8 - b it C o u n te r fS /2 8

7 - b it C o u n te r

O p tio n

Watchdog Timer

C LR

¸2

W D T T im e - o u t

( fS /2 1 6 )

If the WDT oscillator is disabled, the WDT clock may still

come from the instruction clock and operate in the same

manner except that in the HALT state the WDT may stop

counting and lose its protecting purpose. In this situation

the logic can only be restarted by external logic. If the

device operates in a noisy environment, using the

on-chip RC oscillator (WDT OSC) is strongly recom-

mended, since the HALT will stop the system clock.

The WDT overflow under normal operation will initialize

a ²chip reset² and set the status bit TO. Whereas in the

HALT mode, the overflow will initialize a ²warm reset²

wherein only the Program Counter and SP are reset to

zero. To clear the contents of the WDT, three methods

are adopted; external reset (a low level to RES), soft-

ware instructions, or a HALT instruction. The software

instructions include ²CLR WDT² and the other set CLR

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

tion, only one can be active depending on the option -

²CLR WDT times selection option². If the ²CLR WDT² is

selected (i.e. CLRWDT times equal one), any execution

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.

The WDT time-out period is fixed to fs/216, because the

²CLR WDT² or ²CLR WDT1² and ²CLR WDT2²

instructions will clear the whole counter of the WDT.

Power Down Operation - HALT

The HALT mode is initialized by the ²HALT² instruction

and results in the following...

· The system oscillator is turned off but the WDT oscil-

lator keeps running (if the WDT oscillator or the real

time clock is selected).

· The contents of the on-chip RAM and registers remain

unchanged

· The WDT and WDT prescaler will be cleared to zero. If

the WDT clock source is from the RTC/WDT oscilla-

tor, the WDT will remain active, and if the WDT clock

source is fSYS/4, the WDT will stop running.

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

· The PDF flag is set and the TO flag is cleared

The system quits the HALT mode by way 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 examining the TO and PDF flags, the cause

for a chip reset can be determined. The PDF flag is

cleared by system power-up or by executing the ²CLR

WDT² instruction and is set when executing the ²HALT²

instruction. On the other hand, the TO flag is set if the

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

resets the Program Counter and SP, and leaves the oth-

ers 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 options. Awakening from an I/O port stimulus,

the program resumes execution of the next instruction.

On the other hand, awakening from an interrupt, two se-

quence may occur. If the related interrupt is disabled or

the interrupt is enabled but the stack is full, the program

resumes execution at the next instruction. But if the in-

terrupt is enabled, and the stack is not full, the regular in-

terrupt response takes place. When an interrupt request

flag is set before entering the ²HALT² status, the system

cannot be awakened using that interrupt. If wake-up

events occur, it takes 1024 tSYS (system clock period) to

resume normal operation. In other words, a dummy pe-

riod is inserted after the wake-up. If the wake-up results

from an interrupt acknowledgment, the actual interrupt

subroutine execution is delayed by more than one cycle.

However, if the Wake-up results in the next instruction

execution, the execution will be performed 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 may occur:

· RES reset during normal operation

· RES reset during HALT

· WDT time-out reset during normal operation

The WDT time-out during HALT differs from other chip

reset conditions, for it can perform a ²warm reset² that

resets only the Program Counter and SP, leaving the

other circuits at their original state. Some registers re-

main unaffected during any other reset conditions. Most

registers are reset to the ²initial condition² when the re-

Rev. 1.30

11

March 6, 2009

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