W79E217A Datasheet, PDF (96/207 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E217A Data Sheet
12.1.5 Mode 3
Mode 3 is used when an extra 8-bit timer is needed. It has different effect on Timer 0 and Timer 1. TL0
and TH0 become two separate 8 bits counters. TL0 uses the Timer 0 control bits C/T , GATE, TR0,
INT0 and TF0, and it can be used to count clock cycles (clock/12 or clock/4) or falling edges on pin
T0, as determined by C/T (TMOD.2). TH0 becomes a clock-cycle counter (clock/12 or clock/4) and
takes over the Timer 1 enable bit TR1 and overflow flag TF1. In contrast, mode 3 simply freezes Timer
1. If Timer 0 is in mode 3, Timer 1 can still be used in modes 0, 1 and 2, but it no longer has control
over TR1 and TF1. Therefore when Timer 0 is in Mode 3, Timer 1 can only count oscillator cycles, and
it does not have an interrupt or flag. With these limitations, baud rate generation is its most practical
application, but other time-base functions may be achieved by reading the registers.
Figure 12-3: Timer/Counter Mode 3
12.2 Timer/Counter 2
Timer/Counter 2 is a 16-bit up/down-counter equipped with a capture/reload capability. The clock
source for Timer/Counter 2 may be the external T2 pin ( C/ T2 = 1) or the crystal oscillator ( C/ T2 = 0),
divided by 12 or 4. The clock is enabled and disabled by TR2. Timer/Counter 2 runs in one of four
operating modes, each of which is discussed below.
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Publication Release Date: December 14, 2007
Revision A3.0