HT45R35V datasheet(13/42 Pages) HOLTEK

13 / 42 page

HT45R35V

Rev. 1.00

January 15, 2009

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

04H

External Interrupt 1

08H

Timer/Event Counter Overflow

0CH

External RC Oscillation

Converter Interrupt

10H

Interrupt Priority

The EMI, EEI0, EEI1, ETI and ERCOCI bits are all used

to control the enable/disable status of interrupts. These

bits prevent the requested interrupt from being serviced.

Once the interrupt request flags, TF, RCOCF, EIF1 and

EIF0, are all set, they remain in the INTC1 or INTC0 reg-

isters respectively until the interrupts are serviced or

cleared by a software instruction.

It is recommended that a program does not use the

²CALL subroutine² within the interrupt subroutine. Inter-

rupts 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 con-

trolled, the original control sequence may be damaged

once the

²CALL² is executed in the interrupt subroutine.

Oscillator Configuration

Various oscillator options offer the user a wide range of

functions according to their various application require-

ments. Two types of system clocks can be selected

while various clock source options for the Watchdog

Timer are provided for maximum flexibility. All oscillator

options are selected through the configuration options.

The two methods of generating the system clock are:

· External crystal/resonator oscillator

· External RC oscillator

One of these two methods must be selected using the

configuration options.

More information regarding the oscillator is located in

Application Note HA0075E on the Holtek website.

External Crystal/Resonator Oscillator

The simple connection of a crystal across OSC1 and

OSC2 will create the necessary phase shift and feed-

back for oscillation, and will normally not require exter-

nal capacitors. However, for some crystals and most

resonator types, to ensure oscillation and accurate fre-

quency generation, it may be necessary to add two

small value external capacitors, C1 and C2. The exact

values of C1 and C2 should be selected in consultation

with the crystal or resonator manufacturer

¢s specifica-

tion. The external parallel feedback resistor, Rp, is nor-

mally not required but in some cases may be needed to

assist with oscillation start up.

Internal Ca, Cb, Rf Typical Values @ 5V, 25

°C

TBD

Oscillator Internal Component Values

Crystal Oscillator C1 and C2 Values

Crystal Frequency

12MHz

TBD

8MHz

TBD

4MHz

TBD

1MHz

TBD

Note:

1. C1 and C2 values are for guidance only.

2. CL is the crystal manufacturer specified

load capacitor value.

Crystal Recommended Capacitor Values

Resonator C1 and C2 Values

Resonator Frequency

3.58MHz

TBD

1MHz

TBD

455kHz

TBD

Note:

C1 and C2 values are for guidance only.

Resonator Recommended Capacitor Values

O S C 1

O S C 2

R f

T o i n t e r n a l

c i r c u i t s

I n t e r n a l

O s c i l l a t o r

C i r c u i t

C 1

C 2

C a

C b

R p

N o t e : 1 . R p i s n o r m a l l y n o t r e q u i r e d .

2 . A l t h o u g h n o t s h o w n O S C 1 / O S C 2 p i n s h a v e a p a r a s i t i c

c a p a c i t a n c e o f a r o u n d 7 p F .

Crystal/Resonator Oscillator

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