Philips Semiconductors
User’s Manual - Preliminary -
P89LPC906/907/908
TIMERS 0 AND 1
2003 Dec 8
41
5. TIMERS 0 AND 1
The
P89LPC906/907/908
has two general-purpose counter/timers which are similar to the 80C51 Timer 0 and Timer 1. Timer 0
of the
P89LPC907
can be configured to operate either as a timer or event counter (see Figure 5-1). An option to automatically
toggle the T0 pin upon timer overflow has been added. Timer 1 of the
P89LPC907
and both Timer 0 and Timer 1 of the
P89LPC906
and
P89LPC908
devices may only function as timers.
In the “Timer” function, the timer is incremented every PCLK.
In the “Counter” function, the Timer 0 register is incremented in response to a 1-to-0 transition on the external input pin, T0, which
is sampled once during every machine cycle. When the pin is high during one cycle and low in the next cycle, the count is
incremented. The new count value appears in the register during the cycle following the one in which the transition was detected.
Since it takes 2 machine cycles (4 CPU clocks) to recognize a 1-to-0 transition, the maximum count rate is 1/4 of the CPU clock
frequency. There are no restrictions on the duty cycle of the external input signal, but to ensure that a given level is sampled at
least once before it changes, it should be held for at least one full machine cycle.
The “Timer” or “Counter” function is selected by control bit T0C/T in the Special Function Register TMOD. Timer 0 and Timer 1
of the
P89LPC906
and
P89LPC908
, and Timer 1 of the
P89LPC907
have four operating modes (modes 0, 1, 2, and 3), which
are selected by bit-pairs (TnM1, TnM0) in TMOD. Modes 0, 1, 2 and 3 are the same for both Timers. Mode 3 is different. The
operating modes are described later in this section. In addition to these modes, Timer 0 of the
P89LPC907
has mode 6.
Additionally the T0M2 mode bit in TAMOD is used to specify modes with Timer 0 of the
P89LPC907
.
Figure 5-1: Timer/Counter Mode Control register (TMOD)
TMOD
Address: 89h
Not bit addressable
Reset Source(s): Any source
Reset Value:
00000000B
BIT
SYMBOL
FUNCTION
TMOD.7
-
Reserved.
TMOD.6
-
Reserved.
TMOD.5, 4
T1M1,T1M0
Mode Select for Timer 1. These bits are used to determine the Timer 1 mode (see Figure
5-2).
TMOD.3
-
Reserved.
TMOD.2
T0C/T
Timer or Counter Selector for Timer 0. Cleared for Timer operation (input from CCLK). Set
for Counter operation (input from T0 input pin).
P89LPC907.
When writing to this register
on the
P89LPC906
or
P89LPC908
devices, this bit position should be written with a zero.
TMOD.1, 0
T0M1,T0M0
Mode Select for Timer 0. These bits are used to determine the Timer 0 mode (see Figure
5-2). On the
P89LPC907
these bits are used with the T0M2 bit in the TAMOD register to
determine the Timer 0 mode (see Figure 5-2).
7
6
5
4
3
2
1
0
-
-
T1M1
T1M0
-
T0C/T
T0M1
T0M0
Summary of Contents for P89LPC906
Page 30: ...Philips Semiconductors User s Manual Preliminary P89LPC906 907 908 CLOCKS 2003 Dec 8 30 ...
Page 34: ...Philips Semiconductors User s Manual Preliminary P89LPC906 907 908 INTERRUPTS 2003 Dec 8 34 ...
Page 40: ...Philips Semiconductors User s Manual Preliminary P89LPC906 907 908 I O PORTS 2003 Dec 8 40 ...
Page 70: ...Philips Semiconductors User s Manual Preliminary P89LPC906 907 908 UART 2003 Dec 8 70 ...
