am getting some signals from PC printer port which are then received in 89cs51 circuit. It seems to work fine but sometimes the89c51 outputs go low and s89c51 hangs up. I have to reset it again. Any idea whats causing this?
May be the power supply to 89c51 not enough?
There are many reasons for hanging up. It may be due to buggy code, noise, poor design etc...
Show us your design & code so that the exact cause can be known.
With good reason, word files tend to be huge, you can only attach certain file types. Zip files are accepted, so you could always zip the file, or use some other format - but keep it as small as possible.
what is the flow of your program?
Is it possible that error occur during data transmission, and the microcontroller stuck while waiting for remaining data?