RANDOM PAGE
SITE SEARCH
LOG
IN
SIGN UP
HELP

Assembler Port Writing

This is the AQA version closing after June 2019. Visit the the version for Eduqas instead .

To gain access to revision questions, please sign up and log in.

Flash LEDs in Sequence

CTRL+Click here to run the simulator.

Type in the code below or copy and paste it.
Click the "A" button to assemble the code (translate it into binary).
Click the "S" button to step through the program.
Connect the LEDs to PORTB and run this example program.

;===CONNECT LEDs TO PORTB===
INIT:
    MOVW    0x00    ; Eight Outputs
    MOVWR   TRISB   ; Data direction

START: 
    MOVW    0x55    ; Control data
    MOVWR   PORTB   ; Write to port
    NOP             ; Get timing right
    NOP
   
    MOVW    0xAA    ; Control data
    MOVWR   PORTB   ; Write to port
 
    JMP     START

TASK: Alter the program to repeatedly flash each LED in turn going from right to left.

Design Traffic Lights Data

CTRL+Click here to run the simulator.

Type in the code below or copy and paste it.
Click the "A" button to assemble the code (translate it into binary).
Click the "S" button to step through the program.
Connect the Traffic Lights to PORTC and run this example program.

;   CONNECT TRAFFIC LIGHTS TO PORTC
    MOVW    0x00    ; Eight outputs
    MOVWR   TRISC   ; Data direction
START:
    MOVW    0x55    ; This number is wrong
    MOVWR   PORTC   ; Write control data
    NOP             ; Get timing right
    NOP

    MOVW    0xA     ; This number is wrong
    MOVWR   PORTC   ; Write control data
    NOP             ; Get timing right
    NOP

    MOVW    0xC     ; This number is wrong
    MOVWR   PORTC   ; Write control data
    NOP             ; Get timing right
    NOP

    MOVW    0x2     ; This number is wrong
    MOVWR   PORTC   ; Write control data

    JMP     START

TASK: Design corrected control data for the traffic lights. Test your data.

Closed Loop Heater and Thermostat

CTRL+Click here to run the simulator.

Type in the code below or copy and paste it.
Click the "A" button to assemble the code (translate it into binary).
Click the "S" button to step through the program.
Connect the heater to PORTA and run this incomplete example program.

; ===== CONNECT THE HEATER TO PORTA =====
        MOVW    0X1     ; OOOOOOOI
        MOVWR   TRISA   ; SET PORTA I/O
LOOP:
        MOVRW   PORTA   ; READ HEATER PORT
        ANDW    0x1     ; IGNORE BITS 2 TO 7
        SUBW    0x1     ; SEE IF W CONTAINED 1
        JPZ     TOOHOT
        JMP     TOOCOLD

TOOHOT:
; ===== Add two lines here ==============
                        ; HEATER OFF
                        ; WRITE TO HEATER
        JMP     LOOP

TOOCOLD:
; ===== Add two lines here ==============
                        ; HEATER ON
                        ; WRITE TO HEATER
        JMP     LOOP

TASK: Complete the four missing lines to turn the heater on and off.

Seven Segment Display

CTRL+Click here to run the simulator.

Type in the code below or copy and paste it.
Click the "A" button to assemble the code (translate it into binary).
Click the "S" button to step through the program.
Connect the Seven Segment Display to PORTC.

; ===== CONNECT THE DISPLAYS TO PORTC =====
    MOVW    0X00   ; SET 8 PORTC OUTPUTS
    MOVWR   TRISC  ; SET 8 PORTC OUTPUTS
    MOVWR   PORTC  ; CLEAR RIGHT SEGMENTS
    MOVW    0X80   ; CLEAR LEFT SEGMENTS
    MOVWR   PORTC  ; CLEAR LEFT SEGMENTS
START:
    MOVW    0X05
    MOVWR   PORTC
    MOVW    0X85
    MOVWR   PORTC

    MOVW    0X0
    MOVWR   PORTC
    MOVW    0X80
    MOVWR   PORTC
        
    JMP     START

TASK: Count from 0 to 9 (Easy).
TASK: Count from 00 to 99 (Very Hard).

H-Bridge Controller

CTRL+Click here to run the simulator.

Type in the code below or copy and paste it.
Click the "A" button to assemble the code (translate it into binary).
Click the "S" button to step through the program.
Connect the Switches to PORTB.
Connect the H-Bridge Controller to PORTB.

; ===========================================
;       H  Bridge  Motor  Control
;       CONNECT  HBRIDGE TO PORTB
;       CONNECT SWITCHES TO PORTB
; ===========================================
        MOVW    0XF0    ; 4 Inputs & Outputs
        MOVWR   TRISB   ; Set PORTB direction
START:
        MOVRW   PORTB   ; READ PORTB
        ANDW    0X70    ; BIT MASK
        SUBW    0X10    ; TEST S4 CLOSED
        JPZ     FORWARD ; Jump If Closed
        
        JMP     COAST   ; Freewheel
; ===========================================
FORWARD:
        MOVW    0X09    ; Close bits 0 and 3
        MOVWR   PORTB
        JMP     START
; ===========================================
COAST:
        MOVW    0X0     ; Open all switches
        MOVWR   PORTB
        JMP     START
; ===========================================

TASK: Get the motor to run in either direction.
TASK: Set the switches to get a braking effect.

Gray Code Position Control

CTRL+Click here to run the simulator.

Type in the code below or copy and paste it.
Click the "A" button to assemble the code (translate it into binary).
Click the "S" button to step through the program.
Connect the Gray Code Controller to PORTC.
Run the program at a high clock rate or the mechanism will overshoot.

; ================================
; ===== GRAY CODE CONTROLLER =====
; ================================
    MOVW    0X3F    ; OOIIIIII
    MOVWR   TRISC   ; Data direction

FORWARD:
    MOVW    0X40    ; Set bit 6
    MOVWR   PORTC   ; Go right
F_REP:
    MOVRW   PORTC   ; POLL PORTC
    ANDW    0X3F    ; Bit Mask
    SUBW    0X0F    ; Position test
    JPZ     BACKWARD; Position found
    JMP     F_REP   ; Position not found

BACKWARD:
    MOVW    0X80    ; Set bit 7
    MOVWR   PORTC   ; Go left
B_REP:
    MOVRW   PORTC   ; POLL PORTC
    ANDW    0X3F    ; Bit mask
    SUBW    0X03    ; Position test
    JPZ     FORWARD ; Position found
    JMP     B_REP   ; Position not found

TASK: Get it to reverse if it overshoots and hits the end of the scale.

Stepper Motor

CTRL+Click here to run the simulator.

Type in the code below or copy and paste it.
Click the "A" button to assemble the code (translate it into binary).
Click the "S" button to step through the program.
Connect the Stepper Motor to PORTB.

; ====================================
; ===== CONNECT STEPPER TO PORTB =====
; ====================================
start:
    movw    0x1
    movwr   portb
    nop
    nop

    movw    0x2
    movwr   portb
    nop
    nop

    movw    0x4
    movwr   portb
    nop
    nop

    movw    0x8
    movwr   portb 

    jmp     start

TASK: Make the motor run backwards.
TASK: Make the motor run in half steps.

Summing DAC

CTRL+Click here to run the simulator.

Type in the code below or copy and paste it.
Click the "A" button to assemble the code (translate it into binary).
Click the "S" button to step through the program.
Connect the Summing DAC PORTA.

; ================================
; ===== CONNECT DAC TO PORTA =====
; ================================
    movw    0x0
start:
    movwr   porta
    addw    0x1
    jmp     start

The gain of the most significant bit input is one.
The microcontroller digital output voltages are ...
- 0 Volts = Low.
- 5 Volts = High.

TASK: Work out the resolution (smallest step size) of this DAC.
TASK: Work out the values of the other input resistors.
TASK: How many output levels are available from this DAC.

Digital Ramp ADC

CTRL+Click here to run the simulator.

Type in the code below or copy and paste it.
Click the "A" button to assemble the code (translate it into binary).
Click the "S" button to step through the program.
Connect the ADC to PORTA.

; =============================
; = CONNECT RAMP ADC TO PORTA =
; =============================
        jmp     init
; ===== VARIABLES =====
count:  db      0x00
delay:  db      0x30
mask:   db      0x80
; =====================
init:
        movrw   mask
        movwr   trisa
        movw    0x0
        movwr   count
s:
        movrw   count
        movwr   porta
        movrw   porta
        andw    0x80
        jpz     pause
        inc     count
        jmp     s

pause:
        movrw    delay
rep:
        subw    0x1
        jpz     init
        jmp     rep

The gain of the most significant bit input is one.
The microcontroller digital output voltages are ...
- 0 Volts = Low.
- 5 Volts = High.

TASKS:

What are the other resistor values?
What is the resolution of this DAC?
How many output values are possible?
Why is the inverting amplifier needed?
What is the function of the comparator?
Why might the Zener diode be needed?