Thanks Erik, but that is not the point.

there is no pc or uart involved ... no dsub connectors nothing what is usually used

RS232 is used is installed is a must and no chance to change, i would use 485 if i could as i am in this business for about 8 years but the real world out there has a rs232 installed (not a pc2pc connection and no uart stuff, just rs232 drivers and receivers carring some 115kbits/sec signals .... that have nothing to do with a uart, it is just a serial data stream

i knew that i can calculate the allowed cable length of a shielded cable

Lmax = 2400pF / (3x mutual capacitance of the cable)

but this is only true for 19200 and not 115200 so the constant of 2400pF is a problem. this is the value that is allowed for rs232 load up to 20000bits/sec (well in fact it is 2500pF but i have to substract some pF for the input cap of the receiver the connectors ... so 2400pF is a good choice.

so does anybody know how to calculate the allowed length of a cable for RS232 level Signals as

Max-Length = function of ( speed and cable capacitance ) ??????

thanks

Michael Schmitt