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Handshake Solutions
HT80C51 User Manual
Peripheral Modules – Timers 0 and 1
Page 30 of 132
© Philips Electronics N.V. 2005
t
01_clk_i
t1_count_i
t01_int1_n_i
GATE1
TR1
TL1
(8 Bits)
TF1
interrupt
Control
C/T1=1
C/T1=0
TH1
(8 Bits)
Reload
[Figure 10] Timer/counter Mode 2: 8bit auto-reload.
5.2.4.4.
Mode 3
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 11].
TL0 uses the timer 0 control bits: C/T0, GATE0, TR0, t01_int0_n_i and TF0.
TH0 is locked into a timer function (counting timer clocks t01_clk_i) 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 on the counter. With timer 0 in mode
3, an 80C51 can look like it has three timer/counters. 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 port as a
baud rate generator, or in fact, in any application not requiring an interrupt.
t
01_clk_i
t0_count_i
t01_int0_n_i
GATE0
TR0
TL0
(8 Bits)
TF0
int1
Control
C/T0=1
C/T0=0
t01_clk_i
TR1
TH0
(8 Bits)
TF1
int3
[Figure 11] Timer/counter 0 mode 3: Two 8bit counters.
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