AT87F55WD-24AI Atmel, AT87F55WD-24AI Datasheet - Page 12

• Manufacturer Part Number: AT87F55WD-24AI
• Description: IC MICRO CTRL 24MHZ 44PLCC
• Manufacturer: Atmel
• Series: 87Fr

Specifications of AT87F55WD-24AI

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 24MHz
• Connectivity: UART/USART
• Peripherals: WDT
• Number Of I /o: 32
• Program Memory Size: 20KB (20K x 8)
• Program Memory Type: OTP Quick FLASH
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-PLCC
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -
• Data Converters: -
• Other names: AT87F55WD24AI

Baud Rate Generator
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 8.
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
Figure 9. Timer 2 in Clock-Out Mode
12
Mdes 1 and 3 Baud Rates
(T2EX)
P1.0
P1.1
(T2)
AT87F55WD
OSC
TRANSITION
DETECTOR
=
Timer 2 Overflow Rate
----------------------------------------------------------- -
2
16
EXEN2
C/T2 BIT
increments every state time (at 1/2 the oscillator fre-
quency). 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 Figure 8. This
figure is valid only if RCLK or TCLK = 1 in T2CON. Note
that a rollover in TH2 does not set TF2 and will not gener-
ate an interrupt. Note too, that if EXEN2 is set, a 1-to-0
transition in T2EX will set EXF2 but will not cause a reload
from (RCAP2H, RCAP2L) to (TH2, TL2). Thus when Timer
2 is in use as a baud rate generator, T2EX can be used as
an extra external interrupt.
Note that when Timer 2 is running (TR2 = 1) as a timer in
the baud rate generator mode, TH2 or TL2 should not be
read from or written to. Under these conditions, the Timer is
incremented every state time, and the results of a read or
write may not be accurate. The RCAP2 registers may be
read but should not be written to, because a write might
overlap a reload and cause write and/or reload errors. The
timer should be turned off (clear TR2) before accessing the
Timer 2 or RCAP2 registers.
EXF2
TR2
Modes 1 and 3
-------------------------------------- -
Baud Rate
2
=
TIMER 2
INTERRUPT
(8-BITS)
RCAP2L RCAP2H
------------------------------------------------------------------------------------- -
32 x [65536-RCAP2H,RCAP2L)]
TL2
T2OE (T2MOD.1)
Oscillator Frequency
(8-BITS)
TH2