HT13R90

Rev. 1.10

11

July 10, 2007

Oscillator Configuration

There are 2 oscillator circuits within the device.

Both circuits are designed for system clocks, namely the

Internal RC oscillator (IRC) and the external Crystal os-

cillator (ECRY), the choice of which is determined by a

configuration option. When in the standby state, the sys-

tem oscillator stops running and all external signals are

ignored to reduce power.

The Internal RC oscillator provides the most cost effec-

tive method of clock implementation, however, when

compared with the crystal oscillator, the frequency of os-

cillation may vary with VDD, temperature and process

variations. It is therefore not suitable for timing sensitive

operations where an accurate oscillator frequency is de-

sired.

If the Crystal oscillator is selected, a crystal connected

between OSC1 and OSC2 is needed to provide the

feedback and phase shift required for the oscillator. No

other external components are required. Instead of a

crystal, a resonator can also be connected between

OSC1 and OSC2 to obtain the desired frequency refer-

ence, but two external capacitors between OSC1,

OSC2 and ground are required.

Note:

The 32768Hz Oscillator has a quick start up de-

sign. This quick start function should automati-

cally turn off after the clock has stabilised to

reduce power consumption.

The IRC circuit will provide the clock during the

power-on option-loading stage. This is neces-

sary as the choice of crystal or IRC is deter-

mined by the oscillator configuration option in

the OTP memory.

The IRC oscillator contains an adjustment con-

figuration option, to enable the IRC frequency to

be adjusted during device programming. This

option has a total of 7 bits (128 sections).

C r y s t a l O s c i l l a t o r

R C O s c i l l a t o r

O S C 1

O S C 2

O S C 1

O S C 2

Configuration Options

The following table shows the full range of Timer configuration options. All of the options must be defined to ensure

proper system functioning.

Name

Description

Function

OSC

Oscillator type definition

0 = 32768Hz oscillator

1 = Internal RC oscillator

OSCON

Oscillator on/off control in

standby mode

Oscillator switched off

Oscillator remains on

PCR0M

TMR0 prescaler

PCR0 - Output Clock Selection

PCR1M

TMR1 prescaler PCR1 -

output clock selection

TMR0_OV

TMR0_OV/2 ~ TMR0_OV/(2

OMOD

Operating mode selection

MODE 0

- continuous mode

MODE 1

- single period mode

MODE 2

- single pulse mode

OACT

Setup LED0 pin

active high or active low

Active low

Active high

LxACT

LEDx wherex=1or2

active high/low setting

Active low

- low driving LED

Active high

- high driving LED

LxOUT

LEDx Output state

wherex=1or2

None

- no output

When active

- output when the LED0 pin is in an active state

When inactive

- output when the LED0 pin is in an inactive state

Both Active and Inactive

- output when the LED0 pin is in both states