You are using an 8051 derivative, aren't you?

In which case, no you can't.
The 8051 has a standard asynchronous serial port (UART), in which each bit is either '1' or '0' for the whole bit time.

Looks like you have an 80us timeslot, with a proportion either high or low (sorry, I can't quite follow your desription).

Could you do this with a PWM?

Or maybe gate the UART output with a clock signal?


BTW: the symbol for the second is lowercase 's' (uppercase 'S' is for siemens, the unit of conductance)