MICROPROCESSORS

Answer: (i) Driver circuit

Explanation: 8051 I/O pins source/sink only ~mA, insufficient for DC motor (hundreds of mA, inductive). Interfacing requires driver circuit (transistor, MOSFET, L293D/L298 motor driver IC) plus flyback diode, not counter/keyboard/crystal.

5 ms Delay Calculation & Program for P2.3 Pulse (11.0592 MHz)

Machine cycle: Fosc/12 = 11059200/12 = 921600 Hz → Tcy = 1.085 µs. Timer increments every 1.085 µs.
Counts needed for 5 ms = 5ms /1.085us = 4608 decimal = 1200H.
For 16-bit timer mode 1: TH:TL = 10000H - 1200H = EE00H. So TH=0EEH, TL=00H. For mode 1 with auto-reload? Use TL load accordingly. Alternative using 50 counts errors small.
If using Timer 0 mode 1:
TH0 = 0EEH, TL0 = 00H yields 5 ms.
For 5 ms high pulse on P2.3:

ORG 0000H
MAIN: MOV TMOD,#01H ; T0 mode1 16-bit
LOOP: SETB P2.3
      MOV TH0,#0EEH
      MOV TL0,#00H
      SETB TR0
WAIT: JNB TF0,WAIT
      CLR TR0
      CLR TF0
      CLR P2.3     ; after 5ms low (or keep high pulse 5ms)
      MOV TH0,#0EEH
      MOV TL0,#00H
      SETB TR0
WAIT2:JNB TF0,WAIT2
      CLR TR0
      CLR TF0
      SJMP LOOP
END

Alternative C: TH0=0xEE; TL0=0x00; loop. If using 12 MHz crystal, Tcy=1us, counts=5000=1388H, TH=0ECH, TL=78H.
Note: For exact 5ms pulse, set P2.3 high, delay, clear, delay.
If only delay value asked: 4608 counts → EE00H reload.

4-Digit Seven-Segment Display Interface with 8051 + Program to Display 1234

Hardware: Common anode/cathode displays via BCD to 7-seg decoder (7447) or direct port driving via current limiting resistors. Use multiplexing: Segments (a-g,dp) to P0 (8 bits), Digit common (COM1-4) via NPN/ULN2003 to P2.0-P2.3. Or use 8255.

Connections: P0.0-P0.7 → a,b,c,d,e,f,g,+dp (or via 74LS244), P2.0→DIG1, P2.1→DIG2, etc., active low/high depending on type. Use multiplexing: enable one digit at a time ~5 ms persistence.

Program (Assembly) to display 1234:

ORG 0000H
MOV P0,#00H
MOV P2,#00H
MAIN: MOV DPTR,#SEG_TABLE
      MOV R0,#01H ; digit 1 = "1"
      MOV R1,#02H ; digit 2 = "2" etc for demo constant 1234
; Multiplex loop
LOOP: MOV A,#01H ; enable DIG1
      MOV P2,A
      MOV A,#06H ; code for "1" (common cathode 06H) from table
      MOV P0,A
      ACALL DELAY_5MS
      MOV A,#02H ; DIG2
      MOV P2,A
      MOV A,#5BH ; "2"
      MOV P0,A
      ACALL DELAY_5MS
      MOV A,#04H ; DIG3 "3"
      MOV P2,A
      MOV A,#4FH
      MOV P0,A
      ACALL DELAY_5MS
      MOV A,#08H ; DIG4 "4"
      MOV P2,A
      MOV A,#66H
      MOV P0,A
      ACALL DELAY_5MS
      SJMP LOOP
SEG_TABLE: DB 3FH,06H,5BH,4FH,66H,6DH,7DH,07H,7FH,6FH ; 0-9 CC
DELAY_5MS: MOV TH0,#0EEH ; as before
           MOV TL0,#00H
           SETB TR0
W:         JNB TF0,W
           CLR TR0
           CLR TF0
           RET
END

Generic BCD display routine: Fetch BCD nibbles from memory, look up segment codes, multiplex digits sequentially. Time-division multiplexing with persistence gives steady 1234 view.

4×4 Keypad Interfacing with 8051 + Display

Hardware: Rows R1-R4 → P1.0-P1.3 (output), Columns C1-C4 → P1.4-P1.7 (input with pull-ups) or via P2. Keypad matrix 4×4=16 keys (0-9,A-F or 1-9,* #). Supply decoupling, debounce capacitors.

Scanning Algorithm:

1. Drive all rows high.
2. Set one row low at a time, read columns. Column low = key pressed at (row, col).
3. Debounce 20 ms delay, re-read.
4. Compute key code = row*4+col, look up ASCII in table.
5. Display on 7-seg/LCD at P0.

Program sketch (assembly):

SCAN: MOV P1,#0F0H ; rows outputs pull?
ROW_LOOP: MOV A,#0FEH ; row0 low
        MOV P1,A
        MOV A,P1
        ANL A,#0F0H
        CJNE A,#0F0H,FOUND
        ; next row 0FDH etc
FOUND: ; compute
        MOV DPTR,#KEYMAP
        MOVC A,@A+DPTR
        MOV P2,A ; display
        ACALL DEBOUNCE

Display: Send decoded hex to LCD via P0 data + P2 control (RS,RW,EN) or to 7-seg via P0 segments + P2 digit select as in Q38. Multiplex display continuously.
Circuit: P1.0-3 via 470Ω to row lines, P1.4-7 via 10k pull-up to Vcc + column lines, optional 74C922 encoder alternative.

Travelling Light Pattern on Port 0 – 500 ms delay 12MHz

One LED ON at a time moving left→right. Fosc 12MHz → Tcy=1µs, 500ms = 500000 counts = ~7×65536 so use loop with timer + software.

ORG 0000H
MOV P0,#01H ; LED0 ON
MOV TMOD,#01H
LOOP: MOV A,P0
      RL A     ; rotate left -> next LED
      MOV P0,A
      JNB ACC.0,NO_RST ; if wrapped? Actually RL 80H->01H
      ; delay 500ms
      ACALL DELAY500
      SJMP LOOP
DELAY500: ; 500ms via Timer0 loops 50×10ms
      MOV R7,#50
D500L: MOV TH0,#0DCH ; 10ms =10000 counts → DC00H (12MHz Tcy1us, 65536-10000=55536= D8F0? Need compute; here approximated)
       MOV TL0,#00H
       SETB TR0
W:     JNB TF0,W
       CLR TR0
       CLR TF0
       DJNZ R7,D500L
       RET
END
; Corrected 10ms calc: 10000 decimal=2710H, TH= D8H, TL= F0H for 1us tick

C (more accurate using Timer): Loop 500×1ms interrupts, or use Timer ISR with reload. Principle: load 01H to P0, delay, RL A, write.

Calculation: 12MHz → 1 machine cycle 1µs → Timer mode1 16-bit counts to 65536. 500ms needs 500000 counts → 7 overflows + remainder. Easiest: loop 50 times 10ms delay.

4-Digit Seven-Segment Display 0-9 Sequence (1 sec) – Hardware as Q38

Use multiplexed P0 segments + P2 digit select.

ORG 0000H
MOV TMOD,#01H
MAIN: MOV R0,#00H ; digit 0
NEXTDIG: MOV A,R0
       MOV DPTR,#SEG
       MOVC A,@A+DPTR
       MOV P0,A ; segments
       MOV A,R0 ; multiplex? Actually display single digit repeated or multiplex all 4 with same?
       ; For 0-9 counter on all digits, display number as 0000-0009 etc - loop multiplex
       ACALL DELAY_1S_4DIGITS ; time-share
       INC R0
       CJNE R0,#10,NEXTDIG
       SJMP MAIN
SEG: DB 3FH,06H,5BH,4FH,66H,6DH,7DH,07H,7FH,6FH
DELAY_1S: ; via timer outer loop 100×10ms
       MOV R7,#100
L1: MOV TH0,#0D8H
    MOV TL0,#0F0H
    SETB TR0
W: JNB TF0,W
    CLR TR0
    CLR TF0
    DJNZ R7,L1
    RET

Logic: Increment 0-9, look up cathode code, output to multiplexed display, 1 sec delay using Timer0 counts. For 4-digit, drive same code to all digits simultaneously or BCD increment with carry.

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.

Short Notes: Interfacing Stepper Motor – see Q128

Unipolar/Bipolar via ULN2003/L293D to P1, sequence 08-04-02-01, speed via delay, direction via sequence reversal. Needs external 12V, diode protection.

Stepper Motors – Working & Applications

Working: Converts electric pulses to discrete mechanical rotation steps. Stator has multiple coils energized sequentially (full/half/micro-step), rotor (permanent magnet/iron) aligns to magnetic field each pulse, giving precise angular steps (e.g., 1.8° →200 steps/rev for 2-phase). 8051 drives via sequence (as Q128): energize coils in order, no feedback needed (open-loop).

Types: Unipolar (4-5 wires), Bipolar (4 wires), Variable Reluctance.

Applications: Printers, CNC, robotics, cameras, ATMs, medical pumps, textile machines, antenna positioning – where precise position/open-loop control needed, not high speed. Advantages: precise, holding torque, no feedback. Disadvantages: resonance, limited high-speed torque vs servo.