参数资料
型号: ADUC836BCPZ
厂商: Analog Devices Inc
文件页数: 57/80页
文件大小: 0K
描述: IC MCU 62K FLASH ADC/DAC 56LFCSP
标准包装: 1
系列: MicroConverter® ADuC8xx
核心处理器: 8052
芯体尺寸: 8-位
速度: 12.58MHz
连通性: EBI/EMI,I²C,SPI,UART/USART
外围设备: POR,PSM,PWM,温度传感器,WDT
输入/输出数: 34
程序存储器容量: 62KB(62K x 8)
程序存储器类型: 闪存
EEPROM 大小: 4K x 8
RAM 容量: 2.25K x 8
电压 - 电源 (Vcc/Vdd): 2.7 V ~ 5.25 V
数据转换器: A/D 7x16b; D/A 1x12b
振荡器型: 内部
工作温度: -40°C ~ 85°C
封装/外壳: 56-VFQFN 裸露焊盘,CSP
包装: 托盘
ADuC836
–60–
ADuC836
–61–
BAUD RATE GENERATION USING TIMER 3
The high integer dividers in a UART block means that high
speed baud rates are not always possible using some particular
crystals, e.g., using a 12 MHz crystal, a baud rate of 115200 is
not possible.To address this problem, the ADuC836 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 bits to 393216
bits 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 dif-
ferent applications. A block diagram of Timer 3 is shown in
Figure 57.
(1 + T3FD/64)
2
T3 RX/TX
CLOCK
CORE
CLK*
T3EN
RX
CLOCK
TX CLOCK
TIMER 1/TIMER 2
RX CLOCK (FIG 44)
FRACTIONAL
DIVIDER
0
1
TIMER 1/TIMER 2
TX CLOCK (FIG 44)
16
2DIV
*THE CORE CLOCK IS THE OUTPUT OF THE PLL (SEE THE ON-CHIP PLL SECTION)
Figure 57. 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 XXXIII. T3CON SFR Bit Designations
Bit Name
Description
7
T3EN
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.
6
–––
Reserved for Future Use
5
–––
Reserved for Future Use
4
–––
Reserved for Future Use
3
–––
Reserved for Future Use
2
DIV2
Binary Divider Factor
1
DIV1
DIV2 DIV1 DIV0 Bin Divider
0
DIV0
0
1
0
1
2
0
1
0
4
0
1
8
1
0
16
1
0
1
32
1
0
64
1
128
The appropriate value to write to the DIV2-1-0 bits can be cal-
culated using the following formula where fCORE is the output of
the PLL, as described in the On-Chip PLL section. Note that the
DIV value must be rounded down.
DIV
f
Baud Rate
CORE
=
×
( )
log
32
2
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 that the T3FD should
be rounded to the nearest integer.
T FD
f
Baud Rate
CORE
DIV
3
2
64
=
×
Once the values for DIV and T3FD are calculated, the actual
baud rate can be calculated using the following formula:
Actual Baud Rate
f
T FD
CORE
DIV
=
×
+
(
)
2
3
64
For a baud rate of 115200 while operating from the maximum
core frequency (CD = 0), we have:
DIV
T FD
Dh
=
×
(
)
=
×
(
)
×
(
) =
=
log
/
/ log
.
12582912 32 115200
2 1 77 1
3
2 12 582912
2
115200
64 45 22 2
1
Therefore, the actual baud rate is 115439 bits.
Table XXXIV. Commonly Used Baud Rates Using Timer 3
Ideal
%
Baud
CD
DIV
T3CON
T3FD
Error
230400
0
80H
2DH
0.2
115200
0
1
81H
2DH
0.2
115200
1
0
80H
2DH
0.2
57600
0
2
82H
2DH
0.2
57600
1
81H
2DH
0.2
57600
2
0
80H
2DH
0.2
38400
0
3
83H
12H
0.1
38400
1
2
82H
12H
0.1
38400
2
1
81H
12H
0.1
38400
3
0
80H
12H
0.1
19200
0
4
84H
12H
0.1
19200
1
3
83H
12H
0.1
19200
2
82H
12H
0.1
19200
3
1
81H
12H
0.1
19200
4
0
80H
12H
0.1
9600
0
5
85H
12H
0.1
9600
1
4
84H
12H
0.1
9600
2
3
83H
12H
0.1
9600
3
2
82H
12H
0.1
9600
4
1
81H
12H
0.1
9600
5
0
80H
12H
0.1
38400
0
3
83H
12H
0.1
REV. A
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