p89cv51rb2 NXP Semiconductors, p89cv51rb2 Datasheet - Page 31

• Manufacturer Part Number: p89cv51rb2
• Description: P89cv51rb2/rc2/rd2 8-bit 80c51 5 V Low Power 64 Kb Flash Microcontroller With 1 Kb Ram, Spi, 6-clock Cpu With 6/12-clock Peripherals
• Manufacturer: NXP Semiconductors

NXP Semiconductors
P89CV51RB2_RC2_RD2_1
Product data sheet
Fig 13. Timer 2 in Auto reload mode (DCEN = 1)
OSC
T2 pin
6
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
Where SupplyFrequency is either f
(C/T2 = 1).
If EXEN2 = 1, a 16-bit reload can be triggered either by an overflow or by a 1-to-0
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 1.
The microcontroller’s hardware will need three consecutive machine cycles in order to
recognize falling edge on T2EX and set EXF2 = 1: in the first machine cycle pin T2EX 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 1.
In
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.
--------------------------------------------------------------------------- -
65536
Figure
SupplyFrequency
–
C/T2 = 0
C/T2 = 1
RCAP2H RCAP2L
13, DCEN = 1 and Timer 2 is enabled to count up or down. This mode allows pin
TR2
Rev. 01 — 5 October 2007
control
(down-counting reload value)
(up-counting reload value)
RCAP2L RCAP2H
osc
(8-bits)
FFH
TL2
(C/T2 = 0) or frequency of signal on T2 pin
P89CV51RB2/RC2/RD2
(8-bits)
FFH
TH2
underflow
overflow
T2EX pin
80C51 with 1 kB RAM, SPI
count direction
1 = up
0 = down
toggle
TF2
© NXP B.V. 2007. All rights reserved.
002aaa525
EXF2
timer 2
interrupt
Equation
31 of 73
1:
(1)