HT46C47 datasheet(9/39 Pages) HOLTEK

9 / 39 page

HT46R47/HT46C47

Rev. 1.30

May 3, 2004

The A/D converter interrupt is initialized by setting the

A/D converter request flag (ADF; bit 6 of INTC), caused

by an end of A/D conversion. When the interrupt is en-

abled, the stack is not full and the ADF is set, a subrou-

tine call to location 0CH will occur. The related interrupt

request flag (ADF) will be reset and the EMI bit cleared

to disable further interrupts.

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

04H

Timer/Event Counter Overflow

08H

A/D Converter Interrupt

0CH

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

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

flag (ADF), enable timer/event counter bit (ETI), enable

external interrupt bit (EEI), enable A/D converter inter-

rupt 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 in-

terrupts are serviced or cleared by a software instruc-

tion.

It is recommended that a program does not use the

CALL subroutine 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 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 30k

W to 750kW. The system clock, divided

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

chronize external logic. The RC oscillator provides the

most cost effective solution. However, the frequency of

oscillation may vary with VDD, temperatures and the

chip itself due to process variations. It is, therefore, not

suitable for timing sensitive operations where an accu-

rate oscillator frequency is desired.

Bit No.

Label

Function

INTC

(0BH)

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)

Unused bit, read as

²0²

INTC 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

V D D

System Oscillator

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