OK this is a generic reply as I do not know what kind of MCU the uPSD32xx is.

1. In the 8052 Bible in the links on left, refer to the 80c51 FAmily hardware description and to the chapter on Timer0 and Timer1. You will find the relationship between the Oscillator frequency and the way the roll over happens based on the various possible modes. There is a good schematic for every mode.

2. Once you get a hang of how it happens in 8051, apply the logic to your MCU based on its internal clock divisions and modes.

If all this sounds complicated, post a link to the PDF of your MCU and shall see if I can give specific help.

Raghu