I need to measure small portions of time (at least 500us) while using Keil's RTX51 with a System Slice of 20ms. I'm assuming that RTX51 already has a realtime counter that tracks clock ticks (or at least Timer0 overflows) since initialization. Does anyone know the variables/registers it uses for this. I cannot find any reference to tracking time that's less than one System Slice in the RTX manual Normally I would set up another timer to do this tracking but Timer1 and Timer2 are already being used for UART and I2C functions. I have a fall back plan to use Timer1 (even while in use as a baud rate generator) but using system variables would be much cleaner