p89v51rb2 NXP Semiconductors, p89v51rb2 Datasheet - Page 36

• Manufacturer Part Number: p89v51rb2
• Description: 8-bit 80c51 5 V Low Power 16/32/64 Kb Flash Microcontroller With 1 Kb Ram
• Manufacturer: NXP Semiconductors

NXP Semiconductors
P89V51RB2_RC2_RD2_4
Product data sheet
Fig 15. Timer 2 in Baud Rate Generator mode
OSC
T2 pin
TCLK = 1, Timer 2 is used as the UART transmit baud rate generator. RCLK has the same
effect for the UART receive baud rate. With these two bits, the serial port can have
different receive and transmit baud rates – Timer 1 or Timer 2.
Figure 15
The baud rate generation mode is like the auto-reload mode, when a rollover in TH2
causes the Timer 2 registers to be reloaded with the 16-bit value in registers RCAP2H and
RCAP2L, which are preset by software.
The baud rates in modes 1 and 3 are determined by Timer 2’s overflow rate given below:
The timer can be configured for either ‘timer’ or ‘counter’ operation. In many applications,
it is configured for ‘timer' operation (C/T2 = 0). Timer operation is different for Timer 2
when it is being used as a baud rate generator.
Usually, as a timer it would increment every machine cycle (i.e.,
frequency). As a baud rate generator, it increments at the oscillator frequency. Thus the
baud rate formula is as follows:
n = 32 in X1 mode, 16 in X2 mode
Where: (RCAP2H, RCAP2L) = The content of RCAP2H and RCAP2L taken as a 16-bit
unsigned integer.
The Timer 2 as a baud rate generator mode is valid only if RCLK and/or TCLK = 1 in
T2CON register. Note that a rollover in TH2 does not set TF2, and will not generate an
interrupt. Thus, the Timer 2 interrupt does not have to be disabled when Timer 2 is in the
baud rate generator mode. Also if the EXEN2 (T2 external enable flag) is set, a 1-to-0
transition in T2EX (Timer/counter 2 trigger input) will set EXF2 (T2 external flag) but will
T2EX pin
------------------------------------------------------------------------------------------------
n
Modes 1 and 3 baud rates = Timer 2 Overflow Rate / 16
Modes 1 and 3 baud rates =
2
65536
transition
detector
OscillatorFrequency
shows Timer 2 in baud rate generator mode:
–
C/T2 = 0
C/T2 = 1
RCAP2H RCAP2L
EXEN2
Rev. 04 — 1 May 2007
control
TR2
control
EXF2
RCAP2L RCAP2H
(8-bits)
timer 2
interrupt
TL2
P89V51RB2/RC2/RD2
(8-bits)
8-bit microcontrollers with 80C51 core
TH2
reload
TX/RX baud rate
1
002aaa526
6
the oscillator
© NXP B.V. 2007. All rights reserved.
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