P89V51RD2 Philips Semiconductors, P89V51RD2 Datasheet - Page 30

• 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 11. Timer 2 in Capture Mode.
T2 pin
OSC
T2EX pin
7.4.1 Capture mode
¸
6
transition
detector
Table 21:
In the Capture Mode there are two options which are selected by bit EXEN2 in
T2CON. If EXEN2 = 0 Timer 2 is a 16-bit timer or counter (as selected by C/T2 in
T2CON) which upon overflowing sets bit TF2, the Timer 2 overflow bit.
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.
Bit
7 to 2
1
0
C/T2 = 0
C/T2 = 1
EXEN2
T2MOD - Timer 2 mode control register (address C9H) bit description
Symbol
-
T2OE
DCEN
control
TR2
Rev. 01 — 01 March 2004
control
capture
Description
Reserved for future use. Should be set to ‘0’ by user programs.
Timer 2 Output Enable bit. Used in programmable clock-out mode
only.
Down Count Enable bit. When set, this allows Timer 2 to be
configured as an up/down counter.
RCAP2L RCAP2H
(8-bits)
TL2
Figure
(8-bits)
TH2
11.
8-bit microcontrollers with 80C51 core
EXF2
TF2
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
002aaa523
P89V51RD2
interrupt
Timer 2
osc
/6 pulses.
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