problem of skipping characters in serial RS232 plz help?

[ehsanelahimirza]

hi all


i m doing serial communication with PC RS232 using 89C51. 9600 baud rate

i m using code to receive data in hyper terminal which i will send through it.
i.e. loop back.


but problem is there of skiping some characters, after some correct chars. and also some times after 5 to 8 chars i will receive some char which i havnt sent.

plz help me out to get rid of the problem

thanks in advance.

 

[laktronics]

Hi,
Try introducing some delay between characters while sending. Some where there is delay in picking up the characters from the receive buffer.
Regards,
Laktronics

 

[ehsanelahimirza]

problem solved by changing max232

 

[laktronics]

Hi,
I am also interested to know if you had to change 10uF capacitors also to make it work. Also could you find any reason for the failure of MAX 232.

Regards,
Laktronics

 

[umery2k75]

When a controller generates the baud rate for serial communication. You need to have a very precise crystal to do so, or else it skips the character at higher baud rate. I had experienced the same problem. It was skipping characters, then I used the crystal frequency which was best for serial communication. I was using 20Mhz, I switched down to 3.5975 Mhz(some thing, forget the actual frequency) for PIC series of controller. So I got better results, even at higher baud rates. Additionally instead of putting some delay on the character, you can lower your baud rate to around 2400, this also solves the problem sometimes.

One day, I had a very bad experienced with the 232 converter, the IC got partially damaged. It was able to Send the Data, but it was not able to Recieve the Data. I didn't notice this at first, because when I was doing the communication it was working and IC was showing the signs of communication, but the Host unit was not able to answer the Controller. I thought maybe I have done something wrong with the code. On those days, I was also making a lot of changes in my code, so I thought definietly I must have done some changes due to which HOST unit had stop to communicate. I spent a lot of time looking at codes. It took lot of time, while trouble shooting. At the end, I come to know the IC got partially damaged. If this converter get faulty all the whole, then I could have guess it's faulty and I would have replaced the IC, but I wasn't expecting the IC to get partially damaged.

 

[ehsanelahimirza]

Hi,
I am also interested to know if you had to change 10uF capacitors also to make it work. Also could you find any reason for the failure of MAX 232.

Regards,
Laktronics

no u dont need to change capacitors.
10uf work perfectly.
condition which i was told later is that all 4 capacitors should b having same value.

 

[laktronics]

Hi,
Thank you verymuch for the info.
Regards,
Laktronics

 

[Sayem Ahmed]

Let me know details about your project.
I am interested.