P89V51RD2 Philips Semiconductors, P89V51RD2 Datasheet - Page 32

• 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
Fig 13. Timer 2 in Auto Reload mode (DCEN = 1).
OSC
T2 pin
7.4.3 Programmable clock-out
¸
6
In
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.
When a logic 0 is applied at pin T2EX this causes Timer 2 to count down. The timer
will underflow when TL2 and TH2 become equal to the value stored in RCAP2L and
RCAP2H. 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.
A 50% duty cycle clock can be programmed to come out on pin T2 (P1.0). This pin,
besides being a regular I/O pin, has two additional functions. It can be programmed:
To configure the Timer/Counter 2 as a clock generator, bit C/T2 (in T2CON) must be
cleared and bit T20E in T2MOD must be set. Bit TR2 (T2CON.2) also must be set to
start the timer.
The Clock-Out frequency depends on the oscillator frequency and the reload value of
Timer 2 capture registers (RCAP2H, RCAP2L) as shown in Equation 2:
1. To input the external clock for Timer/Counter 2, or
2. To output a 50% duty cycle clock ranging from 122 Hz to 8 MHz at a 16 MHz
Figure
C/T2 = 0
C/T2 = 1
operating frequency.
13, DCEN =
TR2
Rev. 01 — 01 March 2004
control
1
and Timer 2 is enabled to count up or down. This mode
(down counting reload value)
(up counting reload value)
RCAP2L RCAP2H
(8-bits)
FFH
TL2
(8-bits)
FFH
TH2
8-bit microcontrollers with 80C51 core
underflow
overflow
T2EX pin
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
count direction
1 = up
0 = down
002aaa525
P89V51RD2
toggle
TF2
EXF2
interrupt
Timer 2
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