Punit Neb,

Sounds like it is time to drag out the oscilloscope and take a look at your MAX3232 circuit. It may be that you have done something where the charge pump in the level translator just cannot keep up at the 115.2K baud data rate. If there is some issue that causes distress to the MAX3232 many times what happens at lower baud rates the output gets some droop but not enough to put the transmitted signal at so low level of signal that the receiver fails. On the other hand at higher baud rates the charge pump may be completely unable to provide the necessary voltage drive to permit the transmitted signal lines to swing to valid levels to be recognized at the receiver end.

Some things to check and consider:

- Make sure you supply the chip with a VDD that is within the range specified on the data sheet.

- Double check all your connections to make sure that they are correct.

- Make sure to provide for adequate input VDD bypassing directly at the chip's VDD and GND pins.

- Check to make sure that you have used the correct size capacitors for the part.

- If you are using cheap polarized capacitors in the charge pump circuit make sure that the polarity is correct. Better yet dump them and use instead some quality ceramic capacitors.

- Make sure you are not trying to drive some load with one of the transmitter outputs that demands large currents. (ie. a 25 ohm load or a direct connect to the base of a grounded emitter NPN transistor or an LED).

In the end if you hook up the scope to see what is going on whilst trying to send something through the chip you will likely discover what the problem is.

Michael Karas