Stepper Motor Interfacing with 8051 + ALP for Speed/Direction

Hardware: 4-phase unipolar stepper (e.g., 28BYJ-48) requires driver ULN2003 (Darlington) or L293D; 12V supply, common +12V, 4 coils → ULN2003 outputs 1A-4A→ P1.0-P1.3. Diode protection. Bipolar uses L298 with 2 coils.

Sequence (full-step): Wave: 08H→04H→02H→01H→08H (clockwise), reverse anticlockwise 01→02→04→08. Half-step interleaves. Supply via external.

Circuit description: P1.0-P1.3→ULN2003 IN1-4 → OUT1-4 → motor coils, COM to +12V, GND common.

ALP to control speed/direction:

ORG 0000H
MOV TMOD,#01H
MAIN: JB P2.0,CLKWISE ; switch on P2.0 selects direction
      MOV R0,#08H ; start sequence anticlk
ACW:  MOV P1,R0
      ACALL DELAY ; speed control delay value
      RR A
      MOV R0,A
      SJMP MAIN
CLKWISE: MOV A,R0
      MOV P1,A
      ACALL DELAY
      RL A
      MOV R0,A
      SJMP MAIN
DELAY: MOV TH0,#HIGH(-counts) ; variable counts via potentiometer ADC or fixed R7
      ; delay = speed: shorter→faster. Adjust R7 value or TH/TL.
      ; example 10ms per step = 100 steps/sec
      RET
END

Speed: Change delay between steps; shorter delay = faster; Direction: reverse sequence. Use Timer interrupt for precise speed.