AT89LP6440 Atmel Corporation, AT89LP6440 Datasheet - Page 87

• Manufacturer Part Number: AT89LP6440
• Manufacturer: Atmel Corporation

Specifications of AT89LP6440

• Flash (kbytes): 64 Kbytes
• Max. Operating Frequency: 20 MHz
• Cpu: 8051-1C
• Max I/o Pins: 38
• Spi: 1
• Twi (i2c): 1
• Uart: 1
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 153.8
• Sram (kbytes): 4.25
• Eeprom (bytes): 8192
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 3.6
• Timers: 3
• Isp: SPI/OCD
• Watchdog: Yes

16.2
16.2.1
3706C–MICRO–2/11
Baud Rates
Using Timer 1 to Generate Baud Rates
The baud rate in Mode 0 depends on the value of the SMOD1 bit in Special Function Register
PCON.7. If SMOD1 = 0 (the value on reset) and TB8 = 0, the baud rate is 1/4 of the oscillator
frequency. If SMOD1 = 1 and TB8 = 0, the baud rate is 1/2 of the oscillator frequency, as shown
in the following equation:
The baud rate in Mode 2 also depends on the value of the SMOD1 bit. If SMOD1 = 0, the baud
rate is 1/32 of the oscillator frequency. If SMOD1 = 1, the baud rate is 1/16 of the oscillator fre-
quency, as shown in the following equation:
Setting TB8 = 1 in Mode 0 enables Timer 1 as the baud rate generator. When Timer 1 is the
baud rate generator for Mode 0, the baud rates are determined by the Timer 1 overflow rate and
the value of SMOD1 according to the following equation:
The Timer 1 overflow rate normally 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 16-2
lists commonly used baud rates and how they can be obtained from Timer 1.
Modes 1, 3
Baud Rate
Mode 0 Baud Rate
Modes 1, 3
Baud Rate
Mode 0 Baud Rate
Mode 2 Baud Rate
Modes 1, 3
Baud Rate
TB8 = 1
TB8 = 0
=
=
2
------------------- -
2
------------------- -
SMOD1
=
SMOD1
32
32
2
------------------- -
SMOD1
=
32
=
=
2
------------------- -
×
×
SMOD1
2
------------------- -
2
------------------- -
-------------------------------------------------------- -
[
Oscillator Frequency
------------------------------------------------------ -
Oscillator Frequency
SMOD1
SMOD1
4
65536
32
×
4
[
(Timer 1 Overflow Rate)
256
×
×
×
–
(Timer 1 Overflow Rate)
–
(
Oscillator Frequency
Oscillator Frequency
RH1,RL1
(
TH1
)
]
AT89LP3240/6440
)
]
×
×
-------------------- -
TPS
-------------------- -
TPS
1
1
+
+
1
1
87