8051 Timing Counting Calculator

Clock cycle Megahertz (mhz)
Desired timer run time (DRT) Milliseconds (mSec)
Timing TasksStandard 12 time periodsEnhanced 6 clock cyclestime
Single timer
1 / (mhz/12)
1 / (mhz/6)		 uSec
8-bit timer counter
TIC12 * 256 / 1000
TIC6 * 256 / 1000		 mSec
16-bit timer counter
TIC12 * 65536 / 1000
TIC6 * 65536 / 1000		 mSec
8-bit recount value
256 - (DRT / TIC12 * 1000)
256 - (DRT / TIC6 * 1000)		 mSec
16-bit recount value
65536 - (DRT / TIC12 * 1000)
65536 - (DRT / TIC6 * 1000)		 mSec

Mode 0 is a 13-bit timing counting mode, Mode 1 is a 16-bit timing counting mode (the most commonly used mode), Mode 2 is an 8-bit automatic reload initial value counting mode, and Mode 3 is only applicable to T0, dividing the 16-bit T0 into two 8-bit timing counters.