Holtek HT67F86A Application Manuallines

HT67F86A Internal RTC Application Guidelines

HT67F86A Internal RTC Application Guidelines

D/N: AN0448E

Introduction

One special feature of the Holtek 8-bit Flash MCU, the HT67F86A, is that it includes an

ultra-low power consumption RTC oscillator and an LCD driver. To meet the demands for

low power consumption applications, the device’s internal RTC has a standby power

consumption of lower than 1µA at an operating voltage of 3V. The integrated LCD driver

can drive dot matrix LCD display applications of up to 1024 pixels, which can be used with

various display configurations and font settings. With the increasing trends of mobile

device applications such as cellphones and tablets, in addition to being utilised in

industrial control and consumer products, the ultra-low standby power consumption

performance is also an especially important consideration in battery-powered applications.

The MCU’s internal RTC oscillator forms an excellent solution for applications which

require a real time clock function as it reduces the need for an external timing IC with the

resulting reductions in cost and design simplification. This application note will introduce

the Holtek MCU internal RTC oscillator characteristics and application guidelines.

Functional Description

Oscillators

The HT67F86A provides 3 frequency oscillation sources, namely the HXT, HITC and LXT

oscillators. Users can select their desired system frequency, f

program. The LXT provides an f

commonly for applications requiring an RTC real-time clock. Additionally, the MCU can

enter the IDLE2 or SLEEP power saving modes also using the application program to

implement different standby power consumption power down modes. The related

registers are listed in the following table, refer to the Oscillators section in the datasheet

for more detailed information.

Register

Name

SCC CKS2 CKS1 CKS0 — FHS — FHIDEN FSIDEN

HIRCC — — — — HIRC1 HIRC0 HIRCF HIRCEN

HXTC — — — — — HXTM HXTF HXTEN

LXTC — — — — — — LXTF LXTEN

7 6 5 4 3 2 1 0

System Operating Mode Control Registers List

using their application

SYS,

frequency of 32768Hz for various MCU clocks, but more

L

Bit

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HT67F86A Internal RTC Application Guidelines

The clock frequency block diagram is shown as below.

f

H

fH/2

/4

f

H

/8

f

H

f

H

f

H

f

H

/16

/32

/64

CKS2~CKS 0

f

SYS

f

SUB

resistor together with the C1

P

HIRCEN

HXTEN

High Speed

Oscillat or

HIRC

HXT

Low Speed

Oscillat or

LXT

f

LXT

FHS

IDLE2

SLEEP

f

H

Prescaler

f

SUB

LXT Oscillator

The LXT oscillation circuit consists of an external 32768Hz crystal and resistor as well as

capacitor components. The crystal is connected between pins XT1 and XT2. The

frequency accuracy adjustment is implemented by the R

and C2 capacitors. Users should refer to the oscillator specification for the resistance and

capacitance configurations. After power on the LXTEN bit will be in a high state which

enable the LXT oscillator. By examining if the LXTF bit has been set high, it can be

determined if the LXT oscillator is powered up and ready for use. The LXT oscillator

circuit is shown as below.

C1

32. 768kHz

C2

Note : 1. RP, C1 and C 2 ar e required .

2. Al though not shown pi ns have a paras iti c capaci tance of ar ound 7pF .

XT1

R

P

XT2

Internal
Oscillator
Circuit

Internal RC
Oscillator

To internal
circuits

External LXT Oscillator

Time Base Control Register

The HT67F86A provides a Real Time Clock function. A time counting function can be

implemented by configuring the Time Base 0 or Time Base 1 interrupt control bits, TB0E

or TB1E, together with the data memory. The time base function clock source, f

from the f

registers to choose a value within the range of f

. The Time Base frequency division ratio is selected by configuring the

LXT

PSC

/28 ~ f

/215. Refer to the datasheet for

PSC

the related registers and the TB0E and TB1E interrupt addresses.

PSC,

comes

AN0448E V1.00 2/7 January 16, 2017

HT67F86A Internal RTC Application Guidelines

f

LXT

LXT

Low Speed

Oscillat or

IDLE2

SLEEP

f

SUB

f

/4

LXT

1/4 Time Base 0

Prescaler

1/8

f

SUB

f

LXT

TB0 [2:0]

f

LCD

Time Base 1

LCD

LVR

WDT

f

SUB

TB1[2:0]

Device Clock Configuration

TB0ON

f

f

/4

LXT

PSC

Prescaler 0

Prescaler 1

f

PSC

f

PSC

/28~ f

/28~ f

PSC

PSC

TB1ON

15

/2

15

/2

Time Base Interrupt

TB0C Register

Bit 7 6 5 4 3 2 1 0

Name TB0ON — — — — TB02 TB01 TB00
R/W R/W — — — — R/W R/W R/W
POR 0 — — — — 0 0 0

Bit 7 TB0ON: Time Base 0 Enable Control

0: Disable

1: Enable

Bit 6~3 Unimplemented, read as “0”

Bit 2~0 TB02~TB00: Time Base 0 time-out period selection

8

000: 2

/f

PSC

9

001: 2

/f

PSC

10

010: 2

011: 2

100: 2

101: 2

110: 2

111: 2

The f

/f

PSC

11

/f

PSC

12

/f

PSC

13

/f

PSC

14

/f

PSC

15

/f

PSC

is derived from the internal clock source f

PSC

M

U
X

TB0 [2:0]

M
U
X

TB1 [2:0]

Time Base 0 Interrupt

Time Base 1 Interrupt

/4.

LXT

AN0448E V1.00 3/7 January 16, 2017