HT46R48 datasheet(10/42 Pages) HOLTEK

10 / 42 page

HT46R48

Rev. 1.10

March 24, 2006

During the execution of an interrupt subroutine, other in-

terrupt acknowledgments are held until the RETI in-

struction is executed or the EMI bit and the related

interrupt control bit are set to 1 (of course, if the stack is

not full). To return from the interrupt subroutine, RET or

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

an interrupt 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

004H

Timer/Event Counter Overflow

008H

A/D Converter Interrupt

00CH

The timer/event counter interrupt request flag (TF), exter-

nal interrupt request flag (EIF), A/D converter request flag

(ADF), enable timer/event counter bit (ETI), enable exter-

nal interrupt bit (EEI), enable A/D converter interrupt bit

(EADI) and enable master interrupt bit (EMI) constitute

an interrupt control register (INTC) which is located at

0BH in the data memory. EMI, EEI, ETI, EADI are used to

control the enabling/disabling of interrupts. These bits

prevent the requested interrupt from being serviced.

Once the interrupt request flags (TF, EIF, ADF) are set,

they will remain in the INTC register until the interrupts

are serviced or cleared by a software instruction.

It is recommended that a program does not use the CALL

subroutine within the interrupt subroutine. Interrupts of-

ten occur in an unpredictable manner or need to be ser-

viced immediately in some applications. If only one stack

is left and enabling the interrupt is not well controlled, the

original control sequence will be damaged once the

²CALL² operates in the interrupt subroutine.

Oscillator Configuration

There are two oscillator circuits in the microcontroller.

Both are designed for system clocks, namely the RC os-

cillator and the crystal oscillator, which are determined

by the options. No matter what oscillator type is se-

lected, the signal provides the system clock. The HALT

mode stops the system oscillator and ignores an exter-

nal signal to conserve power.

If an RC oscillator is used, an external resistor between

OSC1 and VSS is required and the resistance must

range from 24k

W to 1MW. The system clock, divided by

4, is available on OSC2 with pull-high resistor, which

can be used to synchronize external logic. The RC os-

cillator provides the most cost effective solution. How-

ever, the frequency of oscillation may vary with VDD,

temperatures and the chip itself due to process varia-

tions. 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 required. Instead of a crystal, a resona-

tor can also be connected between OSC1 and OSC2 to

get a frequency reference, but two external capacitors in

OSC1 and OSC2 are required (If the oscillating fre-

quency is less than 1MHz).

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 65

ms at 5V. The WDT oscillator

can be disabled by options 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)

ETI

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

EADI

Controls the A/D converter interrupt (1=enabled; 0=disabled)

EIF

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

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

ADF

A/D converter request flag (1=active; 0=inactive)

For test mode used only.

Must be written as

²0²; otherwise may result in unpredictable operation.

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

f S Y S / 4

O S C 1

V D D

4 7 0 p F

System Oscillator

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