APM 2.5 serial functions

Hello Everyone, I managed to get an APM 2.5 serial connection running between a raspberry pi the APM 2.5

I have successfully armed the board and changed flight modes to the APM via serial command from the Raspbery pi.

I have successfully done

Mode Stabilize
Mode RTL
and Mode Loiter

and throttle arm

But i’m wondering how do I access the PWM output of the output channel to the ESCs? with serial port,
My setup is shown below along with the screenshot of the Rspi that shows the mode has been changed.

my setup can be seen below

diydrones.com/forum/topics/apm-2 … connection

I’m deseperately looking for help