AT89LP216 Atmel Corporation, AT89LP216 Datasheet - Page 40

• Manufacturer Part Number: AT89LP216
• Manufacturer: Atmel Corporation

Specifications of AT89LP216

• Flash (kbytes): 2 Kbytes
• Max. Operating Frequency: 20 MHz
• Cpu: 8051-1C
• Max I/o Pins: 14
• Spi: 1
• Uart: 1
• Sram (kbytes): 0.125
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 2
• Isp: SPI/OCD
• Watchdog: Yes

18. Baud Rates
18.0.1
40
AT89LP216
Using Timer 1 to Generate Baud Rates
The baud rate in Mode 0 is fixed as shown in the following equation:
The baud rate in Mode 2 depends on the value of the SMOD1 bit in Special Function Register
PCON.7. If SMOD1 = 0 (the value on reset), the baud rate is 1/32 of the oscillator frequency. If
SMOD1 = 1, the baud rate is 1/16 of the oscillator frequency, as shown in the following equation:
The Timer 1 overflow rate determines the baud rates in Modes 1 and 3. When Timer 1 is the
baud rate generator, the baud rates are determined by the Timer 1 overflow rate and the value
of SMOD1 according to the following equation:
The Timer 1 interrupt should be disabled in this application. The Timer itself can be configured
for either timer or counter operation in any of its 3 running modes. In the most typical applica-
tions, it is configured for timer operation in auto-reload mode (high nibble of TMOD = 0010B). In
this case, the baud rate is given by the following formula:
Programmers can achieve very low baud rates with Timer 1 by configuring the Timer to run as a
16-bit auto-reload timer (high nibble of TMOD = 0001B). In this case, the baud rate is given by
the following formula.
Table 18-1
lists commonly used baud rates and how they can be obtained from Timer 1.
Modes 1, 3
Modes 1, 3
Baud Rate
Baud Rate
Mode 2 Baud Rate
Modes 1, 3
Baud Rate
Mode 0 Baud Rate
=
=
2
------------------- -
2
------------------- -
=
SMOD1
SMOD1
32
32
2
------------------- -
SMOD1
=
32
×
×
2
------------------- -
SMOD1
Oscillator Frequency
------------------------------------------------------ -
Oscillator Frequency
------------------------------------------------------ -
32
[
=
×
256
[
(Timer 1 Overflow Rate)
Oscillator Frequency
------------------------------------------------------ -
256
×
–
(
(Oscillator Frequency)
–
RH1 RL1
(
TH1
,
2
)
]
)
]
×
×
-------------------- -
TPS
-------------------- -
TPS
1
1
+
+
1
1
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