MDC2250 serial isn't working with a TTL level shifter.... help!

Hi All and thanks in advance.

I have a MDC2250 which I am trying to control with an arduino MEGA and have been failing miserably at! My current setup sets the arduino\'s serial ports to 115200 kbs, reads a command from serial0 (PC interface) and re-broadcasts the command on Serial3.

I have tried a MAX level shifter (forget the exact number, has more channels than the MAX232) to no avail. I CAN control the controller from my laptop using a USB to Serial converter and PuTTY terminal.

I scoped the output of my level shifter and saw that the waveforms were just about identical except for one thing: the USB converter was giving me a clean +/- 10V voltage swing while the MAX chip was giving me a +8V -6.8V swing.

Is the MDC2250\'s serial really that picky about voltage or is there something else possibly going on?

The MDC2250 uses a MAX202, which is practically identical to the MAX232.

It is therefore compatible with the standard rs232 voltage swing with is min -3/+3V at the input. We\'ve seen it work with 0-5V swings. Check the datasheet for that part to verify.