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HT46R14A

A/D Type 8-Bit OTP MCU

Holtek Semiconductor 

HT46R14A

Bit No.

0

1

2

3

4

5

6

7

Label

ET0I

ET1I

EADI

¾

T0F

T1F

ADF

¾

Function

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

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

Control the A/D converter interrupt

Unused bit, read as ²0²

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

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

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

Unused bit, read as ²0²

MFIC (1BH) Register

During the execution of an interrupt subroutine, other in-

terrupt acknowledgements 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, a RET or RETI

instruction may be executed. The RETI instruction will set

the EMI bit to re-enable an interrupt service, but the 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 0

1

004H

External interrupt 1

2

008H

Comparator 0 output interrupt

3 00CH

Comparator 1 output interrupt

4

010H

External interrupt 2 (from PC1)

5

014H

Multi-function interrupt (Timer/

event counter 0/1 & ADC converter)

6

018H

The EMI, EEI0, EEI1, EC0I, ET0I, ET1I, and EMFI are

all used to control the enable/disable status of inter-

rupts. These bits prevent the requested interrupt from

being serviced. Once the interrupt request flags (EI0F,

EI1F, C0F, T0F, T1F, MFI) are all set, they remain in the

INTC1 or INTC0 respectively until the interrupts are ser-

viced or cleared by a software instruction. It is recom-

mended that a program does not use the ²CALL

subroutine² 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 if the ²CALL²

operates within the interrupt subroutine.

Oscillator Configuration

There are two types of system oscillator circuits within the

microcontroller. These are an RC oscillator and a Crys-

tal oscillator, the choice of which is determined via a

configuration option. The Power-down mode stops the

system oscillator and ignores an external signal to con-

serve power.

V DD

O SC1

O SC1

O SC2

fS Y S /4

O SC2

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

C r y s ta l O s c illa to r

R C O s c illa to r

System Oscillator

If an RC oscillator is used, an external resistor between

OSC1 and VSS is required and whose resistance

should range from 24kW to 1MW. Pin OSC2 can be

used to monitor the system frequency at 1/4 the system

frequency or can be used to synchronize external cir-

cuitry. The RC oscillator provides the most cost effec-

tive means of oscillator implementation, however, the

frequency of oscillation may vary with VDD, tempera-

ture and process variations. It is, therefore, not recom-

mended for use in timing sensitive applications where

an accurate oscillator frequency is desired.

If a Crystal oscillator is used, a crystal connected be-

tween OSC1 and OSC2 is required. No other external

components are required. Instead of a crystal, a resona-

tor can also be connected between OSC1 and OSC2 to

obtain a frequency reference, but two external capaci-

tors connected between OSC1, OSC2 and ground are

required, if the oscillating frequency is less than 1MHz.

When the system enters the Power-down mode the sys-

tem oscillator is stopped to conserve power.

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

and no external components are required. Even if the sys-

tem enters the power down mode where the system clock

is stopped, the WDT oscillator will continue to operate with

a period of approximately 65ms at 5V. The WDT oscillator

can be disabled using a configuration option to conserve

power.

Rev. 1.00

11

August 3, 2007

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