diff options
Diffstat (limited to 'roms/7seg_counter_irq_timer.asm')
-rw-r--r-- | roms/7seg_counter_irq_timer.asm | 112 |
1 files changed, 112 insertions, 0 deletions
diff --git a/roms/7seg_counter_irq_timer.asm b/roms/7seg_counter_irq_timer.asm new file mode 100644 index 0000000..29a3b54 --- /dev/null +++ b/roms/7seg_counter_irq_timer.asm @@ -0,0 +1,112 @@ +PORTA = $6001 +DDRA = $6003 +T1LCL = $6004 +T1LCH = $6005 +ACR = $600b +PCR = $600c +IER = $600e +IFR = $600f + +SER = %00000001 +RCLK = %00000010 +SRCLK = %00000100 + +INTERVAL = 33 ; increase counter 3 times per scond + +COUNTER = $0 ; visible counter +TICKS = $3 ; internal ticks counter (on overflow increment counter) + + .org #$f800 + +reset: + sei ; disallow interrupts during initialization + + ldx #$FF ; initialize call stack to $1FF + txs + + lda #%11000010 ; enable CA1 and timer1 interrupts + sta IER + lda #$0 ; negative edge triggering + sta PCR + + lda ACR + AND #$7F + ORA #%01000000 ; setup timer for free running timer1, no PB7 + sta ACR + + lda #%00000111 ; set output on 7seg control pins of PORTA + sta DDRA + + lda #$0 ; initialize 8-bit counter and tick counter + sta COUNTER + lda #INTERVAL + sta TICKS + + lda ACR + + lda #$0F ; initialize counter of VIA timer1 ($270f = 9999 at 1MHz) + sta T1LCL + lda #$27 + sta T1LCH + + cli ; allow interrupts now + +mainloop: ; main loop, just print value of counter + lda COUNTER + jsr print7seg + jmp mainloop + +print7seg: + ldy #$8 ; 8 bits to shift +loop7seg: + rol a + bcc zerobit ; C=0, bang a zero to SER +onebit: + ldx #(SER) ; C=1, bang a one to SER + stx PORTA + ldx #(SER | SRCLK) + stx PORTA + ldx #(SER) + stx PORTA + jmp next +zerobit: + ldx #$0 ; C=0, bang a zero to SER + stx PORTA + ldx #SRCLK + stx PORTA + ldx #$0 + stx PORTA + jmp next +next: + dey + bne loop7seg + rol a ; restore A register +output: + ldx #0 ; bang RCLK to store output in latch + stx PORTA + ldx #RCLK + stx PORTA + ldx #0 + stx PORTA + rts + +nmi: + rti + +irq: + pha + bit T1LCL ; clear timer1 interrupt + bit PORTA ; clear CA1 interrupt + dec TICKS + bne irq_done + lda #INTERVAL + sta TICKS + inc COUNTER +irq_done: + pla + rti + + .org #$fffa + .word nmi + .word reset + .word irq |