IMU 6DOFv2 serial garbage data in ARM processor board

Hi, all.

I connected my IMU6DOFv2 straight from its TX, RX and Gnd (5V TTL) to my ARM prcoessor board thru sparkfun’s recommeded TTL to RS232 converter. However, no matter how I tried, although I verify from my C code, I can make changes to the IMU config menu, but I receive garage data from it everytime.

I use the same code and same conenction and hooked up to my laptop, instead of the ARM processor board, I got correct serial data from the IMU.

My question is, why is it that the IMU6DOFv2 with the TTL to RS232 converter doesn’t work with my ARM board RS232 port. I looked at the scope on the TX line from IMU, it has pulses hovering a few volts (positive). There is no negative volts though, suggest ground. But I am using common ground for all connections.

Anyone help?