2 baud rates – Rainbow Electronics AT89LP214 User Manual
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3538A–MICRO–7/06
AT89LP213/214 [Preliminary]
17.2
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:
17.2.1
Using Timer 1 to Generate Baud Rates
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.
lists commonly used baud rates and how they can be obtained from Timer 1.
Mode 0 Baud Rate
Oscillator Frequency
2
-------------------------------------------------------
=
Mode 2 Baud Rate
2
SMOD1
32
--------------------
(Oscillator Frequency)
×
=
Table 17-2.
Commonly Used Baud Rates Generated by Timer 1 (TPS = 0000B)
Baud Rate
f
OSC
(MHz)
SMOD1
Timer 1
C/T
Mode
Reload Value
Mode 0: 1 MHz
2
X
X
X
X
Mode 2: 375K
12
0
X
X
X
62.5K
12
1
0
2
F4H
19.2K
11.059
1
0
2
DCH
9.6K
11.059
0
0
2
DCH
4.8K
11.059
0
0
2
B8H
2.4K
11.059
0
0
2
70H
1.2K
11.059
0
0
1
FEE0H
137.5
11.986
0
0
1
F55CH
110
6
0
0
1
F958H
110
12
0
0
1
F304H
Modes 1, 3
Baud Rate
2
SMOD1
32
--------------------
(Timer 1 Overflow Rate)
×
=
Modes 1, 3
Baud Rate
2
SMOD1
32
--------------------
Oscillator Frequency
256
TH1
(
)
–
[
]
-------------------------------------------------------
1
TPS
1
+
--------------------
Ч
Ч
=
Modes 1, 3
Baud Rate
2
SMOD1
32
--------------------
Oscillator Frequency
256
R
H1,RL1
(
)
–
[
]
-------------------------------------------------------
×
1
TPS
1
+
--------------------
Ч
=