This calculator is designed to give critical timing values for the 8051 microcontroller's timer 0 and timer 1. Enter the microcontroller clock rate in megahertz and the desired run-time duration in milliseconds of the timer. Click on Calculate. The calculated rates and values are only the run-time of the timer; the general formula is also given. No attempt at calculation of the overhead is made for stopping, starting or loading and reloading of the timers since that time is negligible. 12-clock parts are conventional 8051 derivatives using 12 machine cycles to execute one instruction cycle. Newer but similar devices often are 6-clock parts and instruction cycle time is reduced by 50 percent. They only need 6 machine cycles to execute one instruction cycle.