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Help regarding printf and scanf

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Moderators: Ajay Bhargav, Arun Kumar V, pdi33, Shailesh NAYAK, ۞ TPS ۞, shyam, sashijoseph, ExperimenterUK, DavesGarage

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Amit Kumar Das

Mon Nov 30 2009, 01:48AM

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I am using AT89s52 uC, 11.0592 MHz crystal, 9600 baud rate. I am not getting the output in hyper-terminal whereas Tx and Rx LEDs are glowing during receive and transmit of the data or while pressing the keys in keyboard. I am getting the output in debug terminal. I am enclosing the program below. Could anybody please find out where lies the fault. Thx in advance.

#include <reg51.h>
#include <stdio.h>

void serial_init()
{
SCON=0x50;
TMOD=0x20;
TH1=0xF3;
TR1=1;
TI=1;
}

void main()
{
unsigned char a[8];
serial_init();
printf("\nWELCOME TO OUR WORLD\n");
for(;;)
{
printf("\nENTER TEXT\n");
scanf("%s",&a);
printf("\nYOU HAVE ENTERED:%s\n",a);
}
}

DavesGarage

Mon Nov 30 2009, 09:52AM

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Please show all of your code - you haven't shown the interrupt handler or the putchar() function...

Thanks,

-Dave
"Basic research is what I am doing when I don't know what I am doing"

Ajay Bhargav

Mon Nov 30 2009, 12:15PM

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i dont trust printf and scanf moreover they are not even recommended to use for embedded applications. why don't you write your own simple functions? its really easy to do. check serial tutorial.

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gopi

Tue Dec 01 2009, 10:01AM

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Amit Kumar Das wrote ...

void serial_init()
{
SCON=0x50;
TMOD=0x20;
TH1=0xF3;
TR1=1;
TI=1;
}

In the code you are setting the baud rate for 2215bps but not for 9600bps.
So change " TH1=-3 or 0xfd or 253"

Never cry in front of others...........
Don't give them the pleasure of knowing how much they hurt you.

DavesGarage

Tue Dec 01 2009, 03:10PM

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Here are some helpful links regarding using the printf(...) function:

http://www.keil.com/support/man/docs/c51/c51_printf.htm

http://www.keil.com/support/man/docs/c51/c51_xf_usingprintf.htm

http://www.keil.com/support/docs/867.htm

http://www.keil.com/support/docs/788.htm

The important part here is as follows:

This function is implementation-specific and is based on the operation of the _getkey and putchar functions. These functions, as provided in the standard library, read and write characters using the microcontroller's serial port. Custom functions may use other I/O devices.

and here is your most basic version of putchar()

CODE:

char putchar (char c)  

   {

   while (!TI);

   TI = 0;

   return (SBUF = c);

   }

-Dave
"Basic research is what I am doing when I don't know what I am doing"

Amit Kumar Das

Tue Dec 01 2009, 09:52PM

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Joined: Mon Apr 28 2008, 06:55PM

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Ajay Sir,

Could u plz give an example of how to use your uploaded library which is available at http://www.8051projects.net/downloads7.html, bcoz it is showing error "requires ANSI style prototype" Please give an example of receiving a string also, as it is not included in the library. Thx..

Ajay Bhargav

Wed Dec 02 2009, 12:27PM

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you need to include uart.h file in your code

CODE:

#include "uart.h"

 

do not include the lib file just the c file is sufficient.

for receiving string, you can use uart_receive() function and keep reading till you get a \r from serial port. uart_receive() will read 1 byte from serial port.

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Amit Kumar Das

Wed Dec 02 2009, 02:34PM

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Can u plz correct my program..

#include <uart.h>
unsigned char mybyte;
char str;
void main()
{
uart_init();
P1=0xff;
P2=0x00;
while(1)
{
mybyte=P1;
uart_send("135");
uart_send(mybyte);
mybyte=bit_8 uart_receive();
P2=mybyte;
uart_string("HELLO");
uart_echo();
do{
str=uart_receive();
}while (str=='\r');
}
}

Thx.

DavesGarage

Thu Dec 03 2009, 06:28PM

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Joined: Tue Jan 20 2009, 08:14AM

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Have a look at my thread:

http://www.8051projects.net/forum-t28867-last.html

Download the software, and see if it works on your system. Then, feel free to comment in that thread about your findings...

You sound like you have the right system for my "outsourcing" project

-Dave
"Basic research is what I am doing when I don't know what I am doing"

Amit Kumar Das

Fri Dec 04 2009, 02:27PM

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Joined: Mon Apr 28 2008, 06:55PM

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Dear Daves,

I posted here because the thread link you have posted is showing 'thread not found' at the time of posting. I analysed and tested your program on the hardware with the settings mentioned in the program. It just prints "Keyboard Echo active". There is no echo of the character typed in the hyperterminal. Even in debug the same thing happens. Let me clear what my requirement is, Some character has to be stored in a pointer e.g. mystr="WELCOME TO 8051" which has to be transferred to hyperterminal. Secondly, it has to send value of mydata say, mydata=0x08. Thirdly 8051 has to receive the numbers(typed in the hyperterminal) say value of mybyte as well as mystr, store it in ram using pointers and display it in LCD.