AT89S8253 Atmel Corporation, AT89S8253 Datasheet - Page 18
AT89S8253
Manufacturer Part Number
AT89S8253
Description
Manufacturer
Atmel Corporation
Datasheets
1.AT89S8253.pdf
(60 pages)
2.AT89S8253.pdf
(2 pages)
3.AT89S8253.pdf
(2 pages)
4.AT89S8253.pdf
(2 pages)
Specifications of AT89S8253
Flash (kbytes)
12 Kbytes
Max. Operating Frequency
24 MHz
Cpu
8051-12C
Max I/o Pins
32
Spi
1
Uart
1
Sram (kbytes)
0.25
Eeprom (bytes)
2048
Operating Voltage (vcc)
2.7 to 5.5
Timers
3
Isp
SPI
Watchdog
Yes
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Figure 10-4. Timer 2 in Baud Rate Generator Mode
11. Baud Rate Generator
18
AT89S8253
T2EX PIN
OSC
T2 PIN
÷
Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON
10-2). 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.
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.
2
TRANSITION
DETECTOR
NOTE: OSC. FREQ. IS DIVIDED BY 2, NOT 12
C/T2 = 0
C/T2 = 1
Modes 1 and 3
-------------------------------------- -
Modes 1 and 3 Baud Rates
EXEN2
TR2
Baud Rate
CONTROL
CONTROL
RCAP2H
TH2
=
---------------------------------------------------------------------------------------------- -
32
EXF2
RCAP2L
×
TL2
[
65536
Oscillator Frequency
=
Timer 2 Overflow Rate
----------------------------------------------------------- -
–
INTERRUPT
TIMER 2
(
RCAP2H,RCAP2L
÷
2
"1"
"1"
TIMER 1 OVERFLOW
Figure
16
"0"
"0"
"0"
10-4.
"1"
÷
SMOD1
RCLK
TCLK
÷
16
16
)
]
CLOCK
CLOCK
Rx
Tx
3286P–MICRO–3/10
(Table