at89lp216-20xi ATMEL Corporation, at89lp216-20xi Datasheet - Page 40

• Manufacturer Part Number: at89lp216-20xi
• Description: At89lp216 8-bit Microcontroller With 2k Bytes Flash
• Manufacturer: ATMEL Corporation

17.2
17.2.1
40
Baud Rates
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.
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
3621B–MICRO–11/07