HT47C20 datasheet(14/56 Pages) HOLTEK

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HT47C20

January 18, 2000

Bit No.

Label

Function

INTC0

(0BH)

EMI

Control the master (global) interrupt

(1= enabled; 0= disabled)

EEI

Control the external interrupt

(1= enabled; 0= disabled)

ETBI

Control the time base interrupt

(1= enabled; 0= disabled)

ERTI

Control the real time clock interrupt

(1= enabled; 0= disabled)

EIF

External interrupt request flag

(1= active; 0= inactive)

TBF

Time base request flag

(1= active; 0= inactive)

RTF

Real time clock request flag

(1= active; 0= inactive)

Unused bit, read as ²0²

INTC1

(1EH)

ETI

Control the timer/event counter interrupt

(1= enabled; 0=disabled)

Unused bit, read as ²0²

4TF

Internal timer/event counter request flag

(1= active; 0= inactive)

Unused bit, read as ²0²

INTC register

Once an interrupt subroutine is serviced, all

other interrupts will be blocked (by clearing the

EMI bit). This scheme may prevent any further

interrupt nesting. Other interrupt requests

may happen during this interval, but only the

interrupt request flag is recorded. If a certain

interrupt needs servicing within the service

routine, the EMI bit and the corresponding bit

of INTC0 or INTC1 may be set allow interrupt

nesting. If the stack is full, the interrupt request

will not be acknowledged, even if the related in-

terrupt is enabled, until the SP is decremented.

If immediate service is desired, the stack must

be prevented from becoming full.

All these kinds of interrupt have a wake-up ca-

pability. As an interrupt is serviced, a control

transfer occurs by pushing the program counter

onto the stack and then by branching to subrou-

tines at specified location(s) in the program

memory. Only the program counter is pushed

onto the stack. If the contents of the register

and status register (STATUS) is altered by the

interrupt service program which corrupts the

desired control sequence, the contents must be

saved first.

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