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Interfacing Parallel I/O Ports: Controlling LEDs and Switches with Assembly Language

This lecture covers the principles of parallel interfacing using I/O ports, focusing on how to control LEDs and debounce switches through assembly programming. You'll learn about various parallel port registers and their configuration, such as PTT, DDRT, and PTP. Practical examples include turning on and off LEDs sequentially using an AC relay, as well as managing pushbuttons with debouncing techniques. Key insights into the code structure and flow will enhance your understanding of microcontroller interactions. Ideal for students and hobbyists looking to deepen their embedded systems knowledge.

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Interfacing Parallel I/O Ports: Controlling LEDs and Switches with Assembly Language

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  1. Parallel Ports Lecture L4.1

  2. Parallel Interfacing • Parallel I/O Ports • Using Parallel Ports

  3. Port Integration Module Reference: PIM_9C32 Block Guide V01.06 S12C32PIMV1.pdf

  4. Port and Data Direction Registers

  5. PTT ($240) DDRT($242) PTP ($258) DDRP($25A) PTJ ($268) DDRJ($26A) PTS ($248) DDRS($24A) PORTAD ($8F) Input only PTM ($250) DDRM($252) PORTB ($1) DDRB ($3) PORTE ($8) DDRE ($9) PORTA ($0) DDRA ($2)

  6. Parallel Interfacing • Parallel I/O Ports • Using Parallel Ports

  7. Turning on an LED

  8. Using an AC Relay

  9. LED Example

  10. ; LED example ptp equ $258 ; Port P ddrp equ $25A ; Direction ORG $800 pb_mask db $04 red db $80 yellow db $40 green db $20 red1 db $7F yellow1 db $BF green1 db $DF init ldaa #$E0 ;PP7..PP5 outputs staa ddrp ;PP2 input ldaa #0 staa ptp ;turn off LEDs rts

  11. ORG $4000 main bsr init ;initialize port mn0 ldx #red ;start with red LED mn1 bsr sec_delay ;wait 1 second ldaa ptp oraa 0,x staa ptp ;light next LED inx cpx #$804 bne mn1 ;light red, yellow, green mn2 bsr sec_delay ;wait 1 second ldaa ptp anda 0,x staa ptp ;turn off next LED inx cpx #$807 bne mn2 ;turn off red, yellow, green bra mn0 ;repeat sequence

  12. #include ms_delay.asm init ldaa #$E0 ;PP7..PP5 outputs staa ddrp ;PP2 input ldaa #0 staa ptp ;turn off LEDs rts sec_delay ldy #1000 jsr ms_delay rts

  13. Interfacing a switch input PTJ: equ $268 ; Port J DDRJ: equ $26A ; Direction ldaa PTJ anda #$80 beq sw_down

  14. Debouncing Switch wait_pb_down ldaa ptj anda pb_mask bne wait_pb_down ;wait to push down ldy #3 jsr ms_delay ;debounce delay ldaa ptj anda pb_mask bne wait_pb_down ;wait until still down rts

  15. Debouncing Switch wait_pb_up ldaa ptj anda pb_mask beq wait_pb_up ;wait to release ldy #3 jsr ms_delay ;debounce delay ldaa ptj anda pb_mask beq wait_pb_up ;wait until still up rts

  16. LED – Pushbutton Example

  17. ; LED and pushbutton example ptp equ $258 ; Port P ddrp equ $25A ; Direction ptj equ $268 ; Port J ddrj equ $26A ; Direction ORG $800 pb_mask db $80 red db $80 yellow db $40 green db $20 red1 db $7F yellow1 db $BF green1 db $DF ORG $4000 main bsr init ;initialize port

  18. ORG $4000 main bsr init ;initialize port ldx #red ;start with red LED mn1 bsr wait_pb_down ;wait to push button ldaa ptp oraa 0,x staa ptp ;light next LED bsr wait_pb_up ;wait to release button inx cpx #$804 bne mn1 ;light red, yellow, green mn2 bsr wait_pb_down ;wait to push button ldaa ptp anda 0,x staa ptp ;turn off next LED bsr wait_pb_up ;wait to release button inx cpx #$807 bne mn2 ;turn off red, yellow, green bra main ;repeat sequence

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