80C186EB/80C188EB Microprocessor User's Manual - CEUNES

TIMER/COUNTER UNITWhen configured for internal clocking, the Timer/Counter Unit uses the input pins either to enabletimer counting or to retrigger the associated timer. Externally, a timer increments on low-tohightransitions on its input pin (up to ¼ CLKOUT frequency).Timers 0 and 1 each have a single output pin. Timer output can be either a single pulse, indicatingthe end of a timing cycle, or a variable duty cycle wave. These two output options correspond tosingle maximum count mode and dual maximum count mode, respectively (Figure 9-4). Interruptscan be generated at the end of every timing cycle.Timer 2 has no input or output pins and can be operated only in single maximum count mode(Figure 9-4). It can be used as a free-running clock and as a prescaler to Timers 0 and 1. Timer 2can be clocked only internally, at ¼ CLKOUT frequency. Timer 2 can also generate interrupts atthe end of every timing cycle.Maxcount AMaxcount BDual MaximumCount ModeMaxcount AOne CPUClockSingle MaximumCount ModeA1296-0AFigure 9-4. Timer/Counter Unit Output Modes9.2 PROGRAMMING THE TIMER/COUNTER UNITEach timer has three registers: a Timer Control register (Figure 9-5 and Figure 9-6), a TimerCount register (Figure 9-7) and a Timer Maxcount Compare register (Figure 9-8). Timers 0 and1 also have access to an additional Maxcount Compare register. The Timer Control register controlstimer operation. The Timer Count register holds the current timer count value, and the MaxcountCompare register holds the maximum timer count value.9-6