參數(shù)資料
型號: ADUC831BCP
廠商: ANALOG DEVICES INC
元件分類: 微控制器/微處理器
英文描述: Circular Connector; No. of Contacts:6; Series:LJT07R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:9; Circular Contact Gender:Socket; Circular Shell Style:Jam Nut Receptacle; Insert Arrangement:9-35
中文描述: 8-BIT, FLASH, 16.78 MHz, MICROCONTROLLER, QCC56
封裝: 8 X 8 MM, LEAD FRAME, CSP-56
文件頁數(shù): 58/76頁
文件大?。?/td> 1211K
代理商: ADUC831BCP
REV. 0
–58–
ADuC831
Timer 3 Generated Baud Rates
The high integer dividers in a UART block mean that high speed
baud rates are not always possible using some particular crystals.
For example, using a 12 MHz crystal, a baud rate of 115200 is
not possible. To address this problem, the ADuC831 has added
a dedicated baud rate timer (Timer 3) specifically for generating
highly accurate baud rates.
Timer 3 can be used instead of Timer 1 or Timer 2 for generating
very accurate high speed UART baud rates including 115200
and 230400. Timer 3 also allows a much wider range of baud
rates to be obtained. In fact, every desired bit rate from 12 bit/s
to 393216 bit/s can be generated to within an error of
±
0.8%.
Timer 3 also frees up the other three timers, allowing them to
be used for different applications. A block diagram of Timer 3 is
shown in Figure 54 below.
(1 + T3FD/64)
2
T3 RX/TX
CLOCK
CORE
CLK
T3EN
RX CLOCK
TX CLOCK
TIMER 1/TIMER 2
RX CLOCK (FIG 53)
FRACTIONAL
DIVIDER
0
0
1
1
TIMER 1/TIMER 2
TX CLOCK (FIG 53)
16
2
DIV
Figure 54. Timer 3, UART Baud Rates
Two SFRs (T3CON and T3FD) are used to control Timer 3.
T3CON is the baud rate control SFR, allowing Timer 3 to be
used to set up the UART baud rate, and setting up the binary
divider (DIV).
Table XXVI. T3CON SFR Bit Designations
Bit
Name
Description
7
T3BAUDEN
T3UARTBAUD Enable
Set to enable Timer 3 to generate
the baud rate. When set, PCON.7,
T2CON.4 and T2CON.5 are ignored.
Cleared to let the baud rate be
generated as per a standard 8052.
Binary Divider Factor.
DIV2 DIV1 DIV0 Bin Divider
0 0 0 1
0 0 1 1
0 1 0 1
0 1 1 1
1 0 0 1
1 0 1 1
1 1 0 1
1 1 1 1
6
5
4
3
2
1
0
DIV2
DIV1
DIV0
The appropriate value to write to the DIV2-1-0 bits can be calcu-
lated using the following formula where f
CORE
is the crystal
frequency:
Note: The DIV value must be rounded down.
DIV
f
Baud Rate
log( )
2
32
CORE
=
×
log
T3FD is the fractional divider ratio required to achieve the
required baud rate. We can calculate the appropriate value for
T3FD using the following formula.
Note: T3FD should be rounded to the nearest integer.
T FD
3
f
Baud Rate
CORE
DIV
2
2
=
×
×
Once the values for DIV and T3FD are calculated the actual
baud rate can be calculated using the following formula.
Actual Baud Rate =
2
×
f
2
(T3FD+64)
CORE
DIV
×
For example, to get a baud rate of 115200 while operating at
11.0592 MHz:
DIV
LOG
=
(
=
(
3
2 11059200
2
/
LOG
T FD
H
)
(
)
=
=
)
×
(
)
=
=
11059200
32 115200
2
1 58
.
1
115200
64
32
20
1
/
/
Therefore, the actual baud rate is 115200 bit/s.
Table XXVII. Commonly Used Baud Rates Using Timer 3
Ideal
Baud
%
Error
Crystal
DIV
T3CON
T3FD
230400
115200
57600
38400
19200
9600
11.0592
11.0592
11.0592
11.0592
11.0592
11.0592
0
1
2
3
4
5
80H
81H
82H
83H
84H
85H
20H
20H
20H
08H
08H
08H
0.0
0.0
0.0
0.0
0.0
0.0
230400
115200
57600
38400
19200
9600
12
12
12
12
12
12
0
1
2
3
4
5
80H
81H
82H
83H
84H
85H
28H
28H
28H
0EH
0EH
0EH
0.16
0.16
0.16
0.16
0.16
0.16
230400
115200
57600
38400
19200
9600
14
14
14
14
14
14
0
1
2
3
4
5
80H
81H
82H
83H
84H
85H
3AH
3AH
3AH
1BH
1BH
1BH
0.39
0.39
0.39
0.16
0.16
0.16
230400
115200
57600
38400
19200
9600
16
16
16
16
16
16
1
2
3
3
4
5
81H
82H
83H
83H
84H
85H
05H
05H
05H
28H
28H
28H
0.64
0.64
0.64
0.16
0.16
0.16
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