HT46R652 datasheet(28/47 Pages) HOLTEK

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HT46R652

Rev. 1.00

December 19, 2006

Low Voltage Reset/Detector Functions

A low voltage detector, LVD, and low voltage reset, LVR, functions are implemented within the microcontroller. These

two functions can be enabled/disabled by options. Once the LVD option is enabled, the user can use the RTCC.3 to en-

able/disable (1/0) the LVD circuit and read the LVD detector status (0/1) from RTCC.5; otherwise, the LVD function is

disabled.

The RTCC register definitions are listed below.

Bit No.

Label

Function

0~2

RT0~RT2

8 to 1 multiplexer control inputs to select the real clock prescaler output

LVDC

LVD enable/disable (1/0)

QOSC

32768Hz OSC quick start-up oscillator

0/1: quickly/slowly start

LVDO

LVD detection output (1/0)

1: low voltage detected, read only

6, 7

Unused bit, read as

²0²

RTCC (09H) Register

The LVR has the same effect or function as the external

RES signal which performs a chip reset. During the

HALT state, both LVR and LVD are disabled.

The microcontroller provides a low voltage reset circuit

in order to monitor the supply voltage of the device. If

the supply voltage of the device is within the range

0.9V~VLVR, such as when changing a battery, the LVR

will automatically reset the device internally.

The LVR includes the following specifications:

· The low voltage (0.9V~V

LVR) has to remain in its origi-

nal state for longer than 1ms. If the low voltage state

does not exceed 1ms, the LVR will ignore it and will

not perform a reset function.

· The LVR uses an

²OR² function with the external RES

signal to perform a chip reset.

The relationship between VDD and VLVR is shown below.

Note: VOPR is the voltage range for proper chip

operation with a 4MHz system clock.

5 . 5 V

3 . 0 V

2 . 2 V

0 . 9 V

V D D

V O P R

V L V R

5 . 5 V

V D D

5 . 5 V

V L V R

0 . 9 V

0 V

R e s e t S i g n a l

R e s e t

* 1

* 2

N o r m a l O p e r a t i o n

R e s e t

L V R D e t e c t V o l t a g e

Low Voltage Reset

Note:

*1: To make sure that the system oscillator has stabilized, the SST provides an extra delay of 1024 system

clock pulses before starting normal operation.

*2: Since a low voltage state has to be maintained its original state for over tLVR, therefore after tLVR delay,

the device enters the reset mode.

HT46R652 Datasheet(PDF) 28 Page - Holtek Semiconductor Inc

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