Philips Semiconductors Product data
P89C60X2/61X2
80C51 8-bit Flash microcontroller family
64KB Flash, 512B/1024B RAM
2003 Sep 11
23
TL0
(8 Bits)
TF0
Interrupt
Control
TH0
(8 Bits)
TF1
Interrupt
Control
TR1
INT0 Pin
Timer 0
Gate bit
TR0
SU01620
C/T = 0
C/T
= 1
*d = 6 in 6-clock mode; d = 12 in 12-clock mode.
OSC
÷ d*
OSC
÷ d*
T0 Pin
Figure 7. Timer/Counter 0 Mode 3: Two 8-Bit Counters
TIMER 2 OPERATION
Timer 2
Timer 2 is a 16-bit Timer/Counter which can operate as either an
event timer or an event counter, as selected by C/T
2 in the special
function register T2CON (see Figure 8). Timer 2 has three operating
modes: Capture, Auto-reload (up or down counting), and Baud Rate
Generator, which are selected by bits in the T2CON as shown in
Table 6.
Capture Mode
In the capture mode there are two options which are selected by bit
EXEN2 in T2CON. If EXEN2=0, then timer 2 is a 16-bit timer or
counter (as selected by C/T
2 in T2CON) which, upon overflowing,
sets bit TF2, the timer 2 overflow bit. This bit can be used to
generate an interrupt (by enabling the Timer 2 interrupt bit in the
IE register). If EXEN2=1, Timer 2 operates as described above, but
with the added feature that a 1-to-0 transition at external input T2EX
causes the current value in the Timer 2 registers, TL2 and TH2, to
be captured into registers RCAP2L and RCAP2H, respectively. In
addition, the transition at T2EX causes bit EXF2 in T2CON to be
set, and EXF2 (like TF2) can generate an interrupt (which vectors to
the same location as Timer 2 overflow interrupt. The Timer 2
interrupt service routine can interrogate TF2 and EXF2 to determine
which event caused the interrupt). The capture mode is illustrated in
Figure 9 (There is no reload value for TL2 and TH2 in this mode.
Even when a capture event occurs from T2EX, the counter keeps on
counting T2EX pin transitions or osc/12 (12-clock Mode) or osc/6
(6-clock Mode) pulses).
Auto-Reload Mode (Up or Down Counter)
In the 16-bit auto-reload mode, Timer 2 can be configured as either
a timer or counter (C/T
2 in T2CON), then programmed to count up
or down. The counting direction is determined by bit DCEN (Down
Counter Enable) which is located in the T2MOD register (see
Figure 10). After reset, DCEN=0 which means Timer 2 will default to
counting up. If DCEN is set, Timer 2 can count up or down
depending on the value of the T2EX pin.
Figure 11 shows Timer 2 which will count up automatically since
DCEN=0. In this mode there are two options selected by bit EXEN2
in T2CON register. If EXEN2=0, then Timer 2 counts up to 0FFFFH
and sets the TF2 (Overflow Flag) bit upon overflow. This causes the
Timer 2 registers to be reloaded with the 16-bit value in RCAP2L
and RCAP2H. The values in RCAP2L and RCAP2H are preset by
software.
If EXEN2=1, then a 16-bit reload can be triggered either by an
overflow or by a 1-to-0 transition at input T2EX. This transition also
sets the EXF2 bit. The Timer 2 interrupt, if enabled, can be
generated when either TF2 or EXF2 are 1.
In Figure 12 DCEN=1 which enables Timer 2 to count up or down.
This mode allows pin T2EX to control the direction of count. When a
logic 1 is applied at pin T2EX, Timer 2 will count up. Timer 2 will
overflow at 0FFFFH and set the TF2 flag, which can then generate
an interrupt, if the interrupt is enabled. This timer overflow also
causes the 16-bit value in RCAP2L and RCAP2H to be reloaded
into the timer registers TL2 and TH2.
A logic 0 applied to pin T2EX causes Timer 2 to count down. The
timer will underflow when TL2 and TH2 become equal to the value
stored in RCAP2L and RCAP2H. A Timer 2 underflow sets the TF2
flag and causes 0FFFFH to be reloaded into the timer registers TL2
and TH2.
The external flag EXF2 toggles when Timer 2 underflows or
overflows. This EXF2 bit can be used as a 17th bit of resolution if
needed. The EXF2 flag does not generate an interrupt in this mode
of operation.
