HT46R46 datasheet(34/77 Pages) HOLTEK

34 / 77 page

HT46R46/C46/R47/C47/R48A/C48A/R49

Rev. 1.30

June 5, 2008

Interrupts

Interrupts are an important part of any microcontroller

system. When an external event or an internal function

such as a Timer/Event Counter or an A/D converter re-

quires microcontroller attention, their corresponding in-

terrupt will enforce a temporary suspension of the main

program allowing the microcontroller to direct attention

to their respective needs. Each device in this series con-

tains a single external interrupt and two internal inter-

rupts functions. The external interrupt is controlled by

the action of the external INT pin, while the internal inter-

rupts are controlled by the Timer/Event Counter over-

flow and the A/D converter interrupt.

Interrupt Register

Overall interrupt control, which means interrupt enabling

and request flag setting, is controlled by a single INTC

the appropriate enable bits in this register each individ-

ual interrupt can be enabled or disabled. Also when an

interrupt occurs, the corresponding request flag will be

set by the microcontroller. The global enable flag if

cleared to zero will disable all interrupts.

Interrupt Operation

A Timer/Event Counter overflow, an end of A/D conver-

sion or the external interrupt line being pulled low will all

generate an interrupt request by setting their corre-

sponding request flag, if their appropriate interrupt en-

able bit is set. When this happens, the Program

Counter, which stores the address of the next instruction

to be executed, will be transferred onto the stack. The

Program Counter will then be loaded with a new ad-

dress which will be the value of the corresponding inter-

rupt vector. The microcontroller will then fetch its next

instruction from this interrupt vector. The instruction at

this vector will usually be a JMP statement which will

jump to another section of program which is known as

the interrupt service routine. Here is located the code to

control the appropriate interrupt. The interrupt service

routine must be terminated with a RETI statement,

which retrieves the original Program Counter address

from the stack and allows the microcontroller to continue

with normal execution at the point where the interrupt

occurred.

The various interrupt enable bits, together with their as-

sociated request flags, are shown in the following dia-

gram with their order of priority.

Once an interrupt subroutine is serviced, all the other in-

terrupts will be blocked, as the EMI bit will be cleared au-

tomatically. This will prevent any further interrupt nesting

from occurring. However, if other interrupt requests oc-

cur during this interval, although the interrupt will not be

immediately serviced, the request flag will still be re-

corded. If an interrupt requires immediate servicing

while the program is already in another interrupt service

routine, the EMI bit should be set after entering the rou-

tine, to allow interrupt nesting. If the stack is full, the in-

terrupt request will not be acknowledged, even if the

I N T C R e g i s t e r

M a s t e r I n t e r r u p t G l o b a l E n a b l e

1 : g l o b a l e n a b l e

0 : g l o b a l d i s a b l e

F o r t e s t m o d e u s e o n l y .

M u s t b e w r i t t e n a s " 0 " o t h e r w i s e m a y

r e s u l t i n u n p r e d i c t a b l e o p e r a t i o n

b 7

b 0

E T I

E E I

E M I

T i m e r / E v e n t C o u n t e r I n t e r r u p t E n a b l e

1 : e n a b l e

0 : d i s a b l e

T i m e r / E v e n t C o u n t e r I n t e r r u p t R e q u e s t F l a g

1 : a c t i v e

0 : i n a c t i v e

E I F

T F

E A D I

A D F

A / D C o n v e r t e r I n t e r r u p t E n a b l e

1 : e n a b l e

0 : d i s a b l e

E x t e r n a l I n t e r r u p t E n a b l e

1 : e n a b l e

0 : d i s a b l e

E x t e r n a l I n t e r r u p t R e q u e s t F l a g

1 : a c t i v e

0 : i n a c t i v e

A / D C o n v e r t e r I n t e r r u p t R e q u e s t F l a g

1 : a c t i v e

0 : i n a c t i v e

Interrupt Control Register

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