HT48RA3 datasheet(10/38 Pages) HOLTEK

10 / 38 page

HT48RA3/HT48CA3

Rev. 1.30

October 12, 2007

will occur. The related interrupt request flag (T1F) will be

reset and the EMI bit cleared to disable further inter-

rupts.

During the execution of an interrupt subroutine, other in-

terrupt acknowledge signals are held until the

²RETI² in-

struction is executed or the EMI bit and the related

interrupt control bit are set to 1 (if the stack is not full). To

return from the interrupt subroutine,

²RET² or ²RETI²

may be invoked. RETI will set the EMI bit to enable an in-

terrupt service, but RET will not.

Interrupts, occurring in the interval between the rising

edges of two consecutive T2 pulses, will be serviced on

the latter of the two T2 pulses, if the corresponding inter-

rupts are enabled. In the case of simultaneous requests

the following table shows the priority that is applied.

These can be masked by resetting the EMI bit.

Interrupt Source

Priority

Vector

External Interrupt

04H

Timer/Event Counter 0 Overflow

08H

Timer/Event Counter 1 Overflow

0CH

The Timer/Event Counter 0/1 interrupt request flag

(T0F/T1F), external interrupt request flag (EIF), enable

Timer/Event Counter 0/1 interrupt bit (ET0I/ET1I), en-

able external interrupt bit (EEI) and enable master inter-

rupt bit (EMI) constitute an interrupt control register

(INTC) which is located at 0BH in the data memory. EMI,

EEI, ET0I and ET1I are used to control the enabling/dis-

abling of interrupts. These bits prevent the requested in-

terrupt from being serviced. Once the interrupt request

flags (T0F, T1F, EIF) are set, they will remain in the INTC

software instruction.

It is recommended that a program does not use the

²CALL subroutine² within the interrupt subroutine. In-

terrupts often occur in an unpredictable manner or

need to be serviced immediately in some applications.

If only one stack is left and enabling the interrupt is not

well controlled, the original control sequence will be dam-

aged once the

²CALL² operates in the interrupt subrou-

tine.

Oscillator Configuration

There are 2 oscillator circuits implemented in the mi-

crocontroller.

Both of them are designed for system clocks, namely

the RC oscillator and the crystal oscillator, which are de-

termined by options. No matter what oscillator type is

selected, the signal provides the system clock. The

HALT mode stops the system oscillator and resists the

external signal to conserve power.

If an RC oscillator is used, an external resistor between

OSC1 and VSS is required and the resistance should

range from 100k

W to 820kW. The system clock, divided

by 4, is available on OSC2, which can be used to syn-

chronize external logic. The internal RC oscillator pro-

vides the most cost effective solution. However, the

frequency of oscillation may vary with VDD, tempera-

tures and the chip itself due to process variations. It is,

therefore, not suitable for timing sensitive operations

where an accurate oscillator frequency is desired.

If the crystal oscillator is used, a crystal across OSC1

and OSC2 is needed to provide the feedback and phase

shift required for the oscillator, and no other external

components are demanded. Instead of a crystal, the

resonator can also be connected between OSC1 and

OSC2 to get a frequency reference, but two external ca-

pacitors in OSC1 and OSC2 are required.

The WDT oscillator is a free running on-chip RC oscilla-

tor, and no external components are required. Even if

the system enters the power down mode, the system

clock is stopped, but the WDT oscillator still works with a

period of approximately 90

ms. The WDT oscillator can

be disabled by ROM code option to conserve power.

Bit No.

Label

Function

EMI

Controls the master (global) interrupt (1= enabled; 0= disabled)

EEI

Controls the external interrupt (1= enabled; 0= disabled)

ET0I

Controls the Timer/Event Counter 0 interrupt (1= enabled; 0= disabled)

ET1I

Controls the Timer/Event Counter 1 interrupt (1= enabled; 0= disabled)

EIF

External interrupt request flag (1= active; 0= inactive)

T0F

Internal Timer/Event Counter 0 request flag (1= active; 0= inactive)

T1F

Internal Timer/Event Counter 1 request flag (1= active; 0= inactive)

Unused bit, read as

²0²

INTC (0BH) Register

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

N M O S O p e n D r a i n

O S C 2

f S Y S / 4

O S C 1

System Oscillator

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