ST2202 datasheet(16/65 Pages) ETC

16 / 65 page

Sitronix

ST2202

Ver 2.0a

16/65

2003-May-05

9.1 Port-A Transistion Interrupt

Port-A is designed for the return line inputs of keyboard scan

with transition triggered interrupt and de-bounce option.

Difference between current value and the data kept previously

of Port-A will generate an interrupt request. The last state of

Port-A must be latched before transition, and this can be done

by one read instruction to Port-A. Steps and program example

are shown below.

Operate Port-A interrupt steps:

1. Set input mode.

2. Read Port-A.

3. Clear interrupt request flag (IRPT).

4. Set interrupt enable flag (IEPT).

5. Clear CPU interrupt disable flag (I).

6. Read Port-A before ‘RTI’ instruction in ISR

Example:

STZ

<PCA

; Set input mode.

LDA

#$FF

STA

<PA

; PA be PULL-UP.

LDA

<PA

; Keep last state.

RMB4

<IREQ

; Clear IRQ flag.

SMB4

<IENA

; Enable INT.

CLI

Interrupt subroutine

LDA

<PA

; Keep last state.

RTI

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