P89V51RD2 Philips Semiconductors, P89V51RD2 Datasheet - Page 25

• Manufacturer Part Number: P89V51RD2
• Description: 8-bit 80C51 5 V low power 64 kB Flash microcontroller with 1 kB RAM
• Manufacturer: Philips Semiconductors

Philips Semiconductors
9397 750 12964
Product data
7.3 Timers/counters 0 and 1
The two 16-bit Timer/Counter registers: Timer 0 and Timer 1 can be configured to
operate either as timers or event counters (see
In the ‘Timer’ function, the register is incremented every machine cycle. Thus, one
can think of it as counting machine cycles. Since a machine cycle consists of six
oscillator periods, the count rate is
In the ‘Counter’ function, the register is incremented in response to a 1-to-0 transition
at its corresponding external input pin, T0 or T1. In this function, the external input is
sampled once every machine cycle.
When the samples show a high in one cycle and a low in the next cycle, the count is
incremented. The new count value appears in the register in the machine cycle
following the one in which the transition was detected. Since it takes two machine
cycles (12 oscillator periods) for 1-to-0 transition to be recognized, the maximum
count rate is
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. In addition to
the ‘Timer’ or ‘Counter’ selection, Timer 0 and Timer 1 have four operating modes
from which to select.
The ‘Timer’ or ‘Counter’ function is selected by control bits C/T in the Special
Function Register TMOD. These two Timer/Counters have four operating modes,
which are selected by bit-pairs (M1, M0) in TMOD. Modes 0, 1, and 2 are the same
for both Timers/Counters. Mode 3 is different. The four operating modes are
described in the following text.
Table 12:
Not bit addressable; Reset value: 00000000B; Reset source(s): any source
Table 13:
Bit
Bit
Symbol
T1GATE
TMOD - Timer/Counter mode control register (address 89H) bit allocation
TMOD - Timer/Counter mode control register (address 89H) bit description
Symbol
T1/T0
GATE
C/T
1
7
12
of the oscillator frequency. There are no restrictions on the duty cycle
Rev. 01 — 01 March 2004
T1C/T
6
Description
Bits controlling Timer1/Timer0
Gating control when set. Timer/Counter ‘x’ is enabled only while
‘INTx’ pin is HIGH and ‘TRx’ control pin is set. When cleared,
Timer ‘x’ is enabled whenever ‘TRx’ control bit is set.
Gating Timer or Counter Selector cleared for Timer operation
(input from internal system clock.) Set for Counter operation (input
from ‘Tx’ input pin).
T1M1
5
1
6
of the oscillator frequency.
T1M0
4
8-bit microcontrollers with 80C51 core
Table 12
T0GATE
3
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
and
T0C/T
P89V51RD2
Table
2
13).
T0M1
1
T0M0
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0