HT82K68 datasheet(12/40 Pages) HOLTEK

12 / 40 page

HT82K68E

August 8, 2000

Preliminary

will be serviced on the latter of the two T2

pulses, if the corresponding interrupts are en-

abled. In the case of simultaneous requests, the

following table shows the priority that is ap-

plied. These can be masked by resetting the

EMI bit.

No.

Interrupt Source

Vector

Timer counter overflow

08H

The timer counter interrupt request flag (T0F),

enable timer counter bit (ET0I), and enable

master interrupt bit (EMI) constitute an inter-

rupt control register (INTC) which is located at

0BH in the data memory. EMI, ET0I, are used

to control the enabling/disabling of interrupts.

These bits prevent the requested interrupt

from being serviced. Once the interrupt request

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

INTC register until the interrupts are serviced

or cleared by a software instruction.

It is suggested that a program does not use the

²CALL subroutine² within the interrupt sub-

routine. Because interrupts often occur in an un-

predictable manner or need to be serviced

immediately in some applications, if only one

stack is left and enabling the interrupt is not well

controlled, once the ²CALL subroutine² operates in

the interrupt subroutine it will damage the original

control sequence.

Oscillator configuration

There are two oscillator circuits in HT82K68E.

Both are designed for system clocks; the RC os-

cillator and the Crystal oscillator, which are de-

termined by mask 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.

Bit No.

Label

Function

INTC

(0BH)

EMI

Controls the master (global) interrupt

(1= enabled; 0= disabled)

Undefined, read as "0"; programming must be "0"

ET0I

Controls the timer counter interrupt

(1= enabled; 0= disabled)

Undefined, read as "0"

Undefined, read as "0"; programming must be "0"

T0F

Internal timer counter request flag

(1= active; 0= inactive)

Undefined, read as "0"

Unused bit, read as "0"

INTC register

Crystal Oscillator

RC Oscillator

OSC1

OSC2

OSC1

OSC2

SYS/4

(NMOS Open

Drain Output)

System oscillator

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