On-Chip Peripheral Components
C513AO
User’s Manual
6-22
05.99
6.2.1.5 Mode 3
Mode 3 has different effects on Timer 0 and Timer 1. Timer 1 in Mode 3 simply holds its count. The
effect is the same as setting TR1 = 0. Timer 0 in Mode 3 establishes TL0 and TH0 as two separate
counters. The logic for Mode 3 on Timer 0 is shown in Figure 6-15. TL0 uses the Timer 0 control
bits: C/T, Gate, TR0, INT0, and TF0. TH0 is locked into a timer function (counting machine cycles)
and takes over TR1 and TF1 from Timer 1. Thus, TH0 now controls the “Timer 1” interrupt.
Mode 3 is provided for applications requiring an extra 8-bit timer or counter. When Timer 0 is in
Mode 3, Timer 1 can be turned on and off by switching it in and out of its own Mode 3. Alternatively,
Timer 1 can still be used by the serial channel as a baudrate generator in this or any application not
requiring an interrupt from Timer 1.
Figure 6-15
Timer/Counter 0, Mode 3: Two 8-Bit Timers/Counters
MCS02096
1
&
OSC
C/T = 0
TL0
TF0
C/T = 1
(8 Bits)
TR1
Gate
P3.2/INT0
Control
Interrupt
(8 Bits)
TH0
Interrupt
TF1
Control
TR1
/12
f
OSC
OSC
f
/12
P3.4/T0
÷ 12
=1
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