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interfacing dotmatrix parallel port printer to 8051

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Moderators: Ajay, Junied , abbas1707, Arun Kumar V, pdi33, Shailesh NAYAK, ۞ TPS ۞, shyam, sashijoseph

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irish

Tue May 27 2008, 06:54AM

Registered Member #8091

Joined: Tue May 27 2008, 06:41AM

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i want to interface microcontroller to dotmatrix printer, actually the project is to pass to printer the data for printing in run time through keyboard but in the initial phase i just want to print the data that i have provided in the asm code. here are my schematics and code but its not working. i dont know whether there is a problem in circuitry or the code.
plz help

CODE:

;;;;;CODE;;;;

busy     bit P1.5

strobe   bit P1.4

portData equ P2  

;

        org 0h

start: 

        call word_Welcome ; to print ' Welcome To '

        call enter        ; new line feed       

        call word_Lab     ; to print ' Computer Laboratory '

        call enter        ; new line feed

        ;

quit:   sjmp Quit         ; Hang Forever until reset pressed

;

;===========================================================

;This subroutine is used to print single character

;trough Port Data

;before printing a character,a busy signal must be detected

;till a low logic received, than a strobe ( --__-- ) pulse 

;must be generate to starts printing a character.

;==========================================================

Printchar:

        mov portData,A

        jb busy,$

        setb strobe

        clr strobe

        acall delay

        Setb strobe

        acall delay

        ret

;

delay:  mov R7,#2

del1:   mov R6,#20

        DJNZ R6,$

        DJNZ R7,del1

        ret

;===========================================================

;This subroutine is used to print a text ' Welcome To'

;this subroutine will print character by character till '$'

;character is detected, when this character is detected then

;It's indicated that a text has finished

;===========================================================

word_welcome:

        mov DPTR,#Text_welcome

lagi1:  clr A

        movc A,@A+DPTR

        cjne A,#'$',Print1

        sjmp Out1

Print1: call Printchar

        inc dptr

        call delay

        sjmp lagi1

Out1:   ret                    

;

;================================================================

;This subroutine is used to print a text ' Computer Laboratorium'

;this subroutine will print character by character till '$'

;character is detected, when this character is detected then

;It's indicated that a text has finished

;===============================================================

word_Lab:

        mov DPTR,#Text_lab

lagi2:  clr A

        movc A,@A+DPTR

        cjne A,#'$',Print2

        sjmp Out2

Print2: call Printchar

        inc dptr

        call delay

        sjmp lagi2

Out2:   ret                    

;

Enter:

        mov A,#0dh

        call printchar

        call delay

        mov A,#0ah

        call printchar

        ret

;

Text_welcome:   DB ' Welcome To           $'

Text_Lab:       DB ' Computer Laboratory  $'

end

printer_circuitry.pdf

[ Edited Thu May 29 2008, 12:42AM ]

pdi33

Tue May 27 2008, 02:53PM

Registered Member #1329

Joined: Mon Jun 04 2007, 09:28AM

Posts: 770
Thanked 185 times in 180 posts

hi irish,
ur code looks perfect to me.
the problem is with ur hardware connection of the busy line . just connect the p1.5 line to the pin 11 of the printer connector instead of the pin 16 . pin 16 is the reset (as u have already mentioned and is the input to the printer to reset it and will always remain high unless ur microcontroller pulls it low. So ur uC goes into a infinite loop at the instructin
jb busy,$
as it doesnot receive a low from the printer.

* inspired to develop,developing to inspire *

pdi33

Tue May 27 2008, 03:13PM

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Joined: Mon Jun 04 2007, 09:28AM

Posts: 770
Thanked 185 times in 180 posts

and yes, do not forget to turn off the printer while progrmming through ISP as the MOSI pin of programmer (an active output pin of the programmer) is shorted to the busy pin (also an active output pin from the printer) which is not recommended. Still better shift the busy line to some other port pin say p1.3 to avoid conflict.
good luck

.
If u still do not get any output by connecting the busy line from pin11, try removing it from the printer connector and shorting the busy line of ur uC to ground. Do not worry about data overflow as the modern parallel printers have an inbuilt buffer memory which can store ur small testing data atleast at present for checking purpose.

* inspired to develop,developing to inspire *

irish

Wed May 28 2008, 01:15AM

Registered Member #8091

Joined: Tue May 27 2008, 06:41AM

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actually i m not using the programmer part of the circuit. i have got a burner so i just dump my code onto the uc.
even after making the changes the printer is not printing anything.

also i want to connect a 20x2 lcd with the microcontroller so that what ever is going to the printer for printing also goes to lcd and is visible there.
plz if some 1 can help in this regard, where to connect the lcd in the circuitry and changes in the code.

pdi33

Wed May 28 2008, 04:23AM

Registered Member #1329

Joined: Mon Jun 04 2007, 09:28AM

Posts: 770
Thanked 185 times in 180 posts

remove the instruction
jb busy,$
and try again.
as for the LCD interfacing check the download and tutorial section with the following link
http://www.8051projects.net/downloads5.html
for the code and the link
http://www.8051projects.net/lcd-interfacing/
for the working principle. U can easily extend it with minor modifications once u understand the logic.

* inspired to develop,developing to inspire *

irish

Wed May 28 2008, 08:41PM

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Joined: Tue May 27 2008, 06:41AM

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at last the printer has started printing. thanks to pdi33. now there is a slight problem and that is the printer prints each character twice. example: " wweellccoommee ttoo llaabb"
guidance required in this regard.

pdi33

Wed May 28 2008, 10:46PM

Registered Member #1329

Joined: Mon Jun 04 2007, 09:28AM

Posts: 770
Thanked 185 times in 180 posts

Hi irish,
well, at last it did work

.
Now, about ur secondary problem about double character printing, still ur code seems alright. Try adding pullup resistors to the port1. i.e. a 9 pin resistor SIP (8+1) having a value of 4.7k or 10kohms with the common tied to VCC and the 8 other lines to the port pins. This is because the internal pullups of 89s51 are only weakly pulled high and if the strobe pin of the printer is consuming a little larger current, then ur high level of uC @ port pin may not be reaching the volatge level +5. this may be causing the problem.Just try it out and give feedback.
Sill i feel u have to modify ur hardware as the software looks good to me.

* inspired to develop,developing to inspire *

irish

Thu May 29 2008, 06:08AM

Registered Member #8091

Joined: Tue May 27 2008, 06:41AM

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you mean to tie pull up resistors to the pins of the microcontroller(those 8 pins which i have used for sending data) or to the 8 data lines of the parallel port???and by the common did you mean the common ground of the entire circuit??
also if this 9 pin pull up resistor is not available than what should i do. is there any alternate way???????????

sashijoseph

Thu May 29 2008, 03:33PM

Registered Member #5870

Joined: Mon Feb 04 2008, 06:26PM

Posts: 647
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irish wrote ...

you mean to tie pull up resistors to the pins of the microcontroller(those 8 pins which i have used for sending data)

Yes.....

and by the common did you mean the common ground of the entire circuit??
also if this 9 pin pull up resistor is not available than what should i do. is there any alternate way???????????

Common is the common pin of the SIP resistor.One end of each of the 8 resistors is tied together to form the 9th common pin.This should be tied to Vcc.
If a sip resistor is unavailable,use 8 normal resistors between Vcc and port pins.

btw which change got it working?...... removing the busy check or grounding P1.5 ?

Let there be music........

irish

Thu May 29 2008, 08:32PM

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Joined: Tue May 27 2008, 06:41AM

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no i havnt removed the busy check, i just connected pin 1.5 to pin 11 instead of pin 16. at first it was not working bcz there were some wires short circuited. whn i removed those short circuits it started printing but with that double character prob. i ll check this resistor method to see if it works.