Counter. TL0 uses the Timer 0 control Bits C/T0# and GATE0 in TMOD register, and TR0 and
TF0 in TCON register in the normal manner. TH0 is locked into a Timer function (counting
FTF1/6) and takes over use of the Timer 1 interrupt (TF1) and run control (TR1) Bits. Thus, oper-
ation of Timer 1 is restricted when Timer 0 is in mode 3. Figure 12-7 gives the autoreload period
calculation formulas for both TF0 and TF1 flags.
Figure 12-8. Timer/Counter 0 in Mode 3: Two 8-bit Counters
TIM0
CLOCK
Timer 0
Interrupt
Request
÷ 6
0
1
Overflow
TL0
(8 Bits)
TF0
TCON.5
T0
C/T0#
TMOD.2
INT0
GATE0
TMOD.3
TR0
TCON.4
Timer 1
Interrupt
Request
Overflow
TIM0
CLOCK
TH0
(8 Bits)
÷ 6
TF1
TCON.7
TR1
TCON.6
Figure 12-9. Mode 3 Overflow Period Formula
6
⋅
(256 – TH0)
FTIM0
6
⋅
(256 – TL0)
FTIM0
TF1PER
=
TF0PER
=
12.4 Timer 1
Timer 1 is identical to Timer 0 excepted for Mode 3 which is a hold-count mode. Following com-
ments help to understand the differences:
•
Timer 1 functions as either a Timer or event Counter in three modes of operation. Figure 12-
2 through Figure 12-6 show the logical configuration for modes 0, 1, and 2. Timer 1’s mode
3 is a hold-count mode.
•
Timer 1 is controlled by the four high-order Bits of TMOD register (see Table 41) and Bits 2,
3, 6 and 7 of TCON register (see Figure 40). TMOD register selects the method of Timer
gating (GATE1), Timer or Counter operation (C/T1#) and mode of operation (M11 and M01).
TCON register provides Timer 1 control functions: overflow flag (TF1), run control bit (TR1),
interrupt flag (IE1) and interrupt type control bit (IT1).
•
•
•
•
Timer 1 can serve as the Baud Rate Generator for the Serial Port. Mode 2 is best suited for
this purpose.
For normal Timer operation (GATE1 = 0), setting TR1 allows TL1 to be incremented by the
selected input. Setting GATE1 and TR1 allows external pin INT1 to control Timer operation.
Timer 1 overflow (count rolls over from all 1s to all 0s) sets the TF1 flag generating an
interrupt request.
When Timer 0 is in mode 3, it uses Timer 1’s overflow flag (TF1) and run control bit (TR1).
For this situation, use Timer 1 only for applications that do not require an interrupt (such as a
Baud Rate Generator for the Serial Port) and switch Timer 1 in and out of mode 3 to turn it
off and on.
•
It is important to stop the Timer/Counter before changing modes.
52
AT89C5132
4173E–USB–09/07
ATMEL [ ATMEL ]
