P89LV51RD2 Philips Semiconductors, P89LV51RD2 Datasheet - Page 33

• Manufacturer Part Number: P89LV51RD2
• Description: 8-bit 80C51 3 V low power 64 kB Flash microcontroller with 1 kB RAM
• Manufacturer: Philips Semiconductors

Philips Semiconductors
9397 750 14101
Product data
Fig 12. Timer 2 in Capture Mode.
T2 pin
OSC
T2EX pin
7.4.2 Auto-reload mode (up or down counter)
¸
6
transition
detector
The capture mode is illustrated in
This bit can be used to generate an interrupt (by enabling the Timer 2 interrupt bit in
the IEN0 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.
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 T2 pin transitions or f
Since once loaded contents of RCAP2L and RCAP2H registers are not protected,
once Timer2 interrupt is signalled it has to be serviced before new capture event on
T2EX pin occurs. Otherwise, the next falling edge on T2EX pin will initiate reload of
the current value from TL2 and TH2 to RCAP2L and RCAP2H and consequently
corrupt their content related to previously reported interrupt.
In the 16-bit auto-reload mode, Timer 2 can be configured as either a timer or counter
(via C/T2 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
will default to counting up. If the DCEN bit is set, Timer 2 can count up or down
depending on the value of the T2EX pin.
Figure 13
C/T2 = 0
C/T2 = 1
shows Timer 2 counting up automatically (DCEN = 0).
EXEN2
Table 22
control
Rev. 03 — 11 October 2004
TR2
control
and
capture
Table
RCAP2L RCAP2H
(8-bits)
TL2
23). When reset is applied, DCEN = 0 and Timer 2
Figure
(8-bits)
TH2
12.
8-bit microcontrollers with 80C51 core
EXF2
TF2
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
P89LV51RD2
002aaa523
interrupt
Timer 2
osc
/6 pulses.
33 of 77