AT89S8253-24AC Atmel, AT89S8253-24AC Datasheet - Page 18

• Manufacturer Part Number: AT89S8253-24AC
• Description: IC 8051 MCU FLASH 12K 44TQFP
• Manufacturer: Atmel
• Series: 89Sr

Specifications of AT89S8253-24AC

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 24MHz
• Connectivity: SPI, UART/USART
• Peripherals: POR, WDT
• Number Of I /o: 32
• Program Memory Size: 12KB (12K x 8)
• Program Memory Type: FLASH
• Eeprom Size: 2K x 8
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Oscillator Type: Internal
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 44-TQFP, 44-VQFP
• Data Bus Width: 8 bit
• Data Ram Size: 256 B
• Interface Type: SPI, UART
• Maximum Clock Frequency: 24 MHz
• Number Of Programmable I/os: 32
• Number Of Timers: 3 bit
• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Operating Temperature: + 70 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: 0 C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Data Converters: -
• Lead Free Status / Rohs Status: No

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
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