AT89S8252-16JA ATMEL [ATMEL Corporation], AT89S8252-16JA Datasheet - Page 15

• Manufacturer Part Number: AT89S8252-16JA
• Description: 8-Bit Microcontroller with 8K Bytes Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Figure 4. Timer 2 in Baud Rate Generator Mode
Baud Rate Generator
0401F–MICRO–11/03
T2EX PIN
OSC
T2 PIN
÷
2
TRANSITION
DETECTOR
NOTE: OSC. FREQ. IS DIVIDED BY 2, NOT 12
Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in T2CON
(Table 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
Figure 4.
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 following equation.
The Timer can be configured for either timer or counter operation. In most applications,
it is configured 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.
C/T2 = 0
C/T2 = 1
EXEN2
TR2
CONTROL
CONTROL
Modes 1 and 3
-------------------------------------- -
Modes 1 and 3 Baud Rates
Baud Rate
RCAP2H
TH2
EXF2
=
RCAP2L
---------------------------------------------------------------------------------------------- -
32
TL2
×
[
65536
Oscillator Frequency
INTERRUPT
=
TIMER 2
÷
Timer 2 Overflow Rate
----------------------------------------------------------- -
–
2
(
"1"
"1"
RCAP2H,RCAP2L
TIMER 1 OVERFLOW
"0"
"0"
"0"
16
"1"
÷
SMOD1
RCLK
TCLK
÷
AT89S8252
16
16
)
]
CLOCK
CLOCK
Rx
Tx
15