TRS3232E: Maximum data rate with RL and CL.

See [FAQ] What is the output transition rate for a logic device? (An RS-232 driver uses higher voltages than a logic device, but the principle is the same.)

R_L does not have a large effect.

Hi Leo,

As Clemens answered the bus capacitance has a larger effect. The longer your cable, the more capacitance the bus will be loaded with which can affect the max data rate. The load resistor has some effect but it mainly causes leakage current to occur on the bus when the driver is active. If RL is very low, the charge pumps of RS232 can start to droop so it's best not to have lower RL.

-Bobby

RS-232 drivers are designed for a load of 5 kΩ ± 2 kΩ. Charge pumps have a certain output impedance. When you try to draw too much current out of the output, the output voltage will drop.