HT47C20L datasheet(14/55 Pages) HOLTEK

14 / 55 page

HT47C20L

January 18, 2000

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 programmer may set the EMI bit

and the corresponding bit of INTC0 or INTC1 al-

low interrupt nesting. If the stack is full, the in-

terrupt request will not be acknowledged, even if

the related interrupt 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, followed by a branch to a sub-

routine at specified locations 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.

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 interrupt request flag

(1=active; 0=inactive)

RTF

Real time clock interrupt 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 interrupt request flag

(1=active; 0=inactive)

Unused bit, read as ²0²

INTC Register

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