Rainbow Electronics T89C51CC02 - Manual (Page 53)

Rev.A - May 17, 2001 53
Preliminary
T89C51CC02
12.3.4. Mode 3 (Two 8-bit Timers)
Mode 3 configures Timer 0 such that registers TL0 and TH0 operate as separate 8-bit Timers (see Figure 37). This
mode is provided for applications requiring an additional 8-bit Timer or 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 F
PER
/6) and takes over use of the Timer 1 interrupt (TF1) and run control
(TR1) bits. Thus, operation of Timer 1 is restricted when Timer 0 is in mode 3.
Figure 37. Timer/Counter 0 in Mode 3: Two 8-bit Counters
12.4. Timer 1
Timer 1 is identical to Timer 0 excepted for Mode 3 which is a hold-count mode. Following comments help to
understand the differences:
•
Timer 1 functions as either a Timer or event Counter in three modes of operation. Figure 34 to Figure 36 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 Figure 40) and bits 2, 3, 6 and 7 of
TCON register (see Figure 39). 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 Timer/Counter before changing mode.
12.4.1. Mode 0 (13-bit Timer)
Mode 0 configures Timer 1 as a 13-bit Timer, which is set up as an 8-bit Timer (TH1 register) with a modulo-
32 prescaler implemented with the lower 5 bits of the TL1 register (see Figure 34). The upper 3 bits of TL1 register
are ignored. Prescaler overflow increments TH1 register.
TR0
TCON.4
TF0
TCON.5
INT0#
0
1
GATE0
TMOD.3
Overflow
Timer 0
Interrupt
Request
C/T0#
TMOD.2
TL0
(8 bits)
TR1
TCON.6
TH0
(8 bits)
TF1
TCON.7
Overflow
Timer 1
Interrupt
Request
T0
PERIPH
CLOCK
÷
6
PERIPH
CLOCK
ч
6