AT89C51RC Atmel Corporation, AT89C51RC Datasheet - Page 16

• Manufacturer Part Number: AT89C51RC
• Manufacturer: Atmel Corporation

Specifications of AT89C51RC

• Flash (kbytes): 32 Kbytes
• Max. Operating Frequency: 24 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Uart: 1
• Sram (kbytes): 0.5
• Operating Voltage (vcc): 4.0 to 6.0
• Timers: 3
• Watchdog: Yes

14. Baud Rate Generator
16
AT89C51RC
Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON
5-2). Note that the baud rates for transmit and receive can be different if Timer 2 is used for the
receiver or transmitter and Timer 1 is used for the other function. Setting RCLK and/or TCLK
puts Timer 2 into its baud rate generator mode, as shown in
The baud rate generator mode is similar to the auto-reload mode, in that 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 according to the fol-
lowing equation.
Figure 14-1. Timer 2 in Baud Rate Generator Mode
The Timer can be configured for either timer or counter operation. In most applications, it is con-
figured for timer operation (CP/T2 = 0). The timer operation is different for Timer 2 when it is
used as a baud rate generator. Normally, as a timer, it increments every machine cycle (at 1/12
the oscillator frequency). As a baud rate generator, however, it increments every state time (at
1/2 the oscillator frequency). The baud rate formula is given below.
where (RCAP2H, RCAP2L) is the content of RCAP2H and RCAP2L taken as a 16-bit unsigned
integer.
Timer 2 as a baud rate generator is shown in
TCLK = 1 in T2CON. Note that a rollover in TH2 does not set TF2 and will not generate an inter-
T2EX PIN
OSC
T2 PIN
÷
2
TRANSITION
DETECTOR
Mdes 1 and 3 Baud Rates
Modes 1 and 3
-------------------------------------- -
NOTE: OSC. FREQ. IS DIVIDED BY 2, NOT 12
Baud Rate
C/T2 = 0
C/T2 = 1
EXEN2
TR2
=
CONTROL
CONTROL
------------------------------------------------------------------------------------- -
32 x [65536-RCAP2H,RCAP2L)]
Oscillator Frequency
Figure
RCAP2H
TH2
=
Timer 2 Overflow Rate
----------------------------------------------------------- -
EXF2
RCAP2L
14-1. This figure is valid only if RCLK or
TL2
Figure
16
INTERRUPT
TIMER 2
÷
2
14-1.
"1"
"1"
TIMER 1 OVERFLOW
"0"
"0"
"0"
"1"
÷
SMOD1
RCLK
TCLK
÷
1920D–MICRO–6/08
16
16
CLOCK
CLOCK
Rx
Tx
(Table