1. Interrupt-Driven State Machine
Lecture L4.2a

2. State Machine with Delay

3. Use Real-time Interrupt with 50 ms Period
State
LED
Delay
(sec) S0
Red
0.5 S1
Yellow
1.0 S2
Green
0.75

4. State Machine with Delay

5. Data Structure Variable Value Dtime 1 Num_states 3 Cur_state S0 $8010 S1
$40
S1t 20 S2
$20
S2t 15

6. $7B

7. ; LED state machine example
ptp equ $ ; Port P
ddrp equ $25A ; Direction
ptj equ $ ; Port J
ddrj equ $26A ; Direction
rti_ivec equ $0FF2
crgflg equ $0037
crgint equ $0038
rtictl equ $003b
Note: Should be
$0FF0.
Monitor error

8. ORG $800
dtime db 1
num_states db 3
cur_state db 3
s0 db $80 ;red led
s0t db 10 ;1/2 sec delay
s1 db $40 ;yellow led
s1t db 20 ;1 sec delay
s2 db $20 ;green led
s2t db 15 ;3/4 sec delay

9. ORG $4000
main
jsr portp_init
jsr rti_init
mn1 bra mn1
portp_init
ldaa #$E0 ;PP7..PP5 outputs
staa ddrp
ldaa #0
staa ptp ;leds off
rts
rti_init sei ;disable interrupts
ldaa #$7b
staa rtictl ;set rti to ms
ldaa #$80
staa crgint ;enable r
ldx #rti_intser
stx rti_ivec ;store rti int vector
cli ;enable interrupts

10. rti_intser
ldaa dtime
deca ;dec dtime
bne exit ;if not zero
ldab cur_state
cmpb num_states ; if cur_state = num_state
bne ri1
clrb
stab cur_state ; reset cur_state to 0
ri1 lslb ; ptr = cur_state * 2
ldx #s0 ; x -> state 0
abx ; x -> next state
ldaa 0,x ; get state value
staa ptp ; and display it
inc cur_state ; update cur_state
ldaa 1,x ; get delay time
exit staa dtime ; and store it in dtime
ldaa #$80
staa crgflg ;clear rti flag
rti

11. ORG $800
dtime db 1
num_states db 3
cur_state db 3
s0 db $80 ;red led
s0t db 10 ;1/2 sec delay
s1 db $40 ;yellow led
s1t db 20 ;1 sec delay
s2 db $20 ;green led
s2t db 15 ;3/4 sec delay