st2024c Sitronix Technology Corporation, st2024c Datasheet - Page 15

• Manufacturer Part Number: st2024c
• Description: 24k 8-bit Single Chip Microcontroller
• Manufacturer: Sitronix Technology Corporation

10.2.4 Port-A interrupt
Port-A, a programmable I/O, can be used as a port interrupt
when it is in the input mode. Any edge transition of the
Port-A input pin will generate an interrupt request. The last
state of Port-A must be kept before I/O transition and this
can be accomplished by reading Port-A.
Operating Port-A interrupt step by step :
Ver 2.2
1.
2.
3.
4.
5.
6.
Set input mode.
Read Port-A.
Clear interrupt request flag (IRPT).
Set interrupt enable flag (IEPT).
Clear CPU interrupt disable flag (I).
Read Port-A before ‘RTI’ instruction in
INT-Subroutine.
PCA[0]
PCA[1]
PCA[2]
PCA[3]
RDPA
PA[1]
PA[2]
PA[3]
PA[0]
D
CK
D
CK
D
CK
D
CK
DFF
DFF
DFF
DFF
Q
Q
Q
Q
FIGURE 10-2: Port Interrupt Logic Diagram
XNOR2
XNOR2
XNOR2
XNOR2
OR2
OR2
OR2
OR2
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When programmer enables INTX and PT interrupts, PA0
trigger occur. INTX and PT interrupts will therefore happen
sequentially. Please refer to the Figure 9-2.
Example :
INT-SUBROUTINE
PCA[4]
PCA[5]
PCA[6]
PCA[7]
PA[4]
PA[5]
PA[6]
PA[7]
STZ
LDA
STA
LDA
RMB4
SMB4
CLI
LDA
RTI
.
.
.
.
.
.
.
D
CK
D
CK
D
CK
CK
D
DFF
DFF
DFF
DFF
NAND8
Q
Q
Q
Q
PCA
#$FF
PA
PA
<IREQ
<IENA
PA
XNOR2
XNOR2
XNOR2
XNOR2
PTIR
High Level Interrupt
OR2
OR2
OR2
OR2
;Set input mode.
;PA be PULL-UP.
;Keep last state.
;Clear IRQ flag.
;Enable INT.
;Keep last state.
ST2024C
1/31/08