P89V51RB2_09 Datasheet, PDF (35/80 Pages) NXP Semiconductors – 8-bit 80C51 5 V low power 16/32/64 kB flash microcontroller with 1 kB RAM

NXP Semiconductors
P89V51RB2/RC2/RD2
8-bit microcontrollers with 80C51 core
(down-counting reload value)
FFH
FFH
toggle
EXF2
OSC
÷6
T2 pin
C/T2 = 0
C/T2 = 1
control
TL2
TH2 ^underflow
(8-bits) (8-bits) _overflow
TF2
timer 2
interrupt
TR2
RCAP2L RCAP2H
count direction
1 = up
0 = down
(up-counting reload value)
T2EX pin
002aaa525
Fig 14. Timer 2 in Auto Reload mode (DCEN = 1)
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.
6.5.3 Programmable clock-out
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:
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
operating frequency.
To configure the Timer/counter 2 as a clock generator, bit C/T2 (in T2CON) must be
cleared and bit T2OE 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:
2^-----×^-----(^--6^---5^--O-5^---3^-s--6^-c---i∠^--l--l(^--a-R^--t--Co^----rA--F--P^--r--2^-e---Hq^---u-,^---eR---n-C^--c---Ay^----P^----2^---L^----)^---)
(2)
Where (RCAP2H,RCAP2L) = the content of RCAP2H and RCAP2L taken as a 16-bit
unsigned integer.
In the Clock-Out mode Timer 2 roll-overs will not generate an interrupt. This is similar to
when it is used as a baud-rate generator.
6.5.4 Baud rate generator mode
Bits TCLK and/or RCLK in T2CON allow the UART) transmit and receive baud rates to be
derived from either Timer 1 or Timer 2 (See Section 6.6 “UARTs” on page 37 for details).
When TCLK = 0, Timer 1 is used as the UART transmit baud rate generator. When
P89V51RB2_RC2_RD2_5
Product data sheet
Rev. 05 — 12 November 2009
© NXP B.V. 2009. All rights reserved.
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