RS232 signal causing interference to audio line

Obviously nothing to do with Keil software tools!

Are you sure it's the RS232?
Conducted, radiated, or what?

Anyhow, you should never run anything digital close to any sensitive analogue signals...

Is your audio well-screened, all you power supplies well-decoupled, etc, etc...?

Obviously nothing to do with Keil software tools!

Are you sure it's the RS232?
Conducted, radiated, or what?

Anyhow, you should never run anything digital close to any sensitive analogue signals...

Is your audio well-screened, all you power supplies well-decoupled, etc, etc...?

answers.

yes it is rs232.
i think it is radiated but is it conducted?
it is well screened.

i use keil for the rs232

"yes it is rs232"

How do you know that?

I mean, how are you certain that it is specifically the RS232 signals that are causing the interference?
What tests have you done to confirm it?

"i use keil for the rs232"

No, you use Keil for loading & reading SBUF.
Interference between physical signals is entirely a hardware issue - nothing to do with your software development tools!

No, you use Keil for loading & reading SBUF.

not really.

you use your hardware, programmed by Keil for loading & reading SBUF.

Erik