P89V51RD2 Philips Semiconductors, P89V51RD2 Datasheet - Page 31

• 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 12. Timer 2 in auto-reload mode (DCEN = 0)
OSC
T2 pin
T2EX pin
7.4.2 Auto-reload mode (up or down counter)
¸
6
transition
detector
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 12
In this mode, there are two options selected by bit EXEN2 in T2CON register. If
EXEN2 = 0, then Timer 2 counts up to 0FFFFH and sets the TF2 (Overflow Flag) bit
upon overflow. This causes the Timer 2 registers to be reloaded with the 16-bit value
in RCAP2L and RCAP2H. The values in RCAP2L and RCAP2H are preset by
software means.
Auto reload frequency when Timer 2 is counting up can be determined from this
formula:
Where SupplyFrequency is either f
(C/T2 =
If EXEN2 =
transition at input T2EX. This transition also sets the EXF2 bit. The Timer 2 interrupt,
if enabled, can be generated when either TF2 or EXF2 is
Microcontroller’s hardware will need three consecutive machine cycles in order to
recognize falling edge on T2EX and set EXF2 =
has to be sampled as ‘1’; in the second machine cycle it has to be sampled as ‘0’, and
in the third machine cycle EXF2 will be set to
------------------------------------------------------------------------------- -
65536
C/T2 = 0
C/T2 = 1
SupplyFrequency
1
).
RCAP2H RCAP2L
shows Timer 2 counting up automatically (DCEN = 0).
EXEN2
1
, a 16-bit reload can be triggered either by an overflow or by a 1-to-0
Table 20
control
TR2
Rev. 01 — 01 March 2004
control
and
reload
Table
RCAP2L RCAP2H
(8-bits)
TL2
21). When reset is applied, DCEN = 0 and Timer 2
osc
(C/T2 = 0) or frequency of signal on T2 pin
(8-bits)
TH2
8-bit microcontrollers with 80C51 core
‘1’
.
1
: in the first machine cycle pin T2EX
EXF2
TF2
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
‘1’
002aaa524
.
P89V51RD2
interrupt
Timer 2
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(1)