Programmable Peripheral Interface (ppi) – 8255a King Saud

programmable peripheral interface (ppi) – 8255a king saud

; Program the 82C55 for Port A and Port B are output ports in mode 0 MOV DX, 703H ; Address of Command Port into DX MOV AL, 80H ; 80H Data into AL OUT DX, AL ; Write 80H into Command Port to program PPI ; An assembly language procedure that multiplexes the 8-digit display. ; This procedure must be called often enough for the display to appear stable DISP PROC NEAR USES AX BX DX SI PUSHF MOV BX, 8 ;load counter BX with # of display digits MOV AH, 01111111B ;load initial digit selection pattern to enable MS digit MOV SI, OFFSET MEM - 1 ;Load SI with offset (MEM) - 1 MOV DX, 701H ;address Port B (for Port A: decrement DX) ;Sequentially display all 8 digits starting with MS digit .