Parallel Port Interfacing

A parallel port is a type of socket found on personal computers for interfacing with various peripherals. It is also known as a printer port.

PC parallel port is 25 pin, D-shaped female connector in the back of the computer. Not all 25 are needed always. Usually you can easily do with only 8 output pins (data lines) and signal ground.

The original IBM-PC’s parallel port had a total of 12 digital outputs and 5 digital inputs accessed via 3 consecutive 8-bit ports in the processor’s I/O space.

Pin out:

Pin description:

You can not directly access the parallel port in windows xp, vista etc due to the security purpose. To access the port do the following:

1. first go to the BIOS setting.

2. then select advanced option.

3. under this option select peripheral configuration

4. then change the setting of parallel port as

a. enable

b. bi-diractional

c. IRQ-7

After doing these steps download the user port and follow the instructions. A window will open, when you will run userport.exe, asking the range.

To find this:

1. right click on my computer icon
2. select manage
3. from device manager select ports(com &LPT)
4. double click on printer port
5. a window will open, choose the resources tab you will find

Fill this range in both the spaces and then click on add button. Then click on start button three times, a message will appear just click ok.

Now your port is ready for interfacing.

Tutorial one:

LED Chaser:

• Connect 8 LEDs to the data port of the parallel port as shown in the figure.
  

• Connect ground to pin # 25.
• Copy and paste the assembly program link it (in MASM) & create .exe file.
• This program is basically LED chaser in which LEDs blink from left to right when you press ‘r’ and from right to left when you press ‘l’. to off these LEDs just press ‘ 0’ and ‘Esc’ button to exit.

Assembly code:

Dosseg

.model small

.stack 100h

.data

msg db 13,10,'Press r for right movement',13,10,'Press l for left movement',13,10, 'Press 0 to Off',13,10, 'Press Esc to exit','$'

.code

main proc

mov ax,@data

mov ds,ax

mov ah,09h

lea dx,msg

int 21h

set: mov al, 0ffh

mov dx, 378h

out dx,al

call delay

call delay

call delay

mov al,00h

out dx,al

call delay

call delay

call delay

mov al,10000000b

lop1:

push ax

push dx

mov ah,06h

mov dl,0ffh

int 21h

cmp al,27

je exit

cmp al,'0'

je off

cmp al,'r'

je loop2

pop dx

pop ax

ror al,1

ror al,1

out dx,al

call delay

call delay

jmp lop1

loop2:

mov dx,378h

mov al,01h

strt: out dx,al

call delay

call delay

rol al,1

rol al,1

push ax

push dx

mov ah,06h

mov dl,0ffh

int 21h

cmp al,27

je exit

cmp al,'0'

je off

cmp al,'l'

je set

pop dx

pop ax

jmp strt

off: mov al, 0h

mov dx, 378h

out dx, al

exit: mov ax, 4c00h

int 21h

main endp

delay proc

push ax

push dx

mov bx,00h

mov ah,2ch ;To Get System Time

int 21h

mov bh,dl ;Copy seconds into bh reg

getsec: mov ah,2ch

int 21h

cmp bh,dl

jne back ;Jump to back when get 1 sec.

jmp getsec

back: pop dx

pop ax

ret

delay endp

end main

• Tutorial two:
  

• Seven Segment Common Cathode Counter:

• Common Cathode means all –ve terminals of LEDs are grounded & 1 for on, 0 for off.

• Connect 8 LEDs to the data port of the parallel port as shown in the figure.
  

• 1^st construct the table for 7-segment

Digits	Hex
0	3f
1	06
2	5b
3	4f
4	66
5	6d
6	7d
7	07
8	7f
9	6f

• This is basically 7-segment counter & timer in which you can set/reset, and pause it.

• If any one interested in this, he can ask me about the assembly code of this project.

Enjoy playing with parallel port.