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.