C517A_99 Datasheet, PDF (87/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C517A
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 seperate
counters. The logic for mode 3 on timer 0 is shown in figure 6-12. 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 the use of 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 out of and into its own mode 3, or can still be used
by the serial channel as a baud rate generator, or in fact, in any application not requiring an interrupt
from timer 1 itself.
OSC
P3.4/T0
=1
Gate
P3.2/INT0
÷ 12
f _OSC /12
C/T = 0
TL0
(8 Bits)
C/T = 1
Control
TR1
&
1
f _OSC /12
TR1
TR1
TH0
(8 Bits)
Control
Figure 6-12
Timer/Counter 0, Mode 3: Two 8-Bit Timers/Counters
Interrupt
TF0
Interrupt
TF1
MCS02096
Semiconductor Group
6-21