參數(shù)資料
型號： ADUC848BSZ8-3
廠商： Analog Devices Inc
文件頁數(shù)： 91/108頁
文件大?。?/td> 0K
描述： IC MCU FLASH W/16BIT ADC 52MQFP
標(biāo)準(zhǔn)包裝： 96
系列： MicroConverter® ADuC8xx
核心處理器： 8052
芯體尺寸： 8-位
速度： 12.58MHz
連通性： I²C，SPI，UART/USART
外圍設(shè)備： POR，PSM，PWM，溫度傳感器，WDT
輸入/輸出數(shù)： 34
程序存儲器容量： 8KB（8K x 8）
程序存儲器類型： 閃存
EEPROM 大?。?/td> 4K x 8
RAM 容量： 2.25K x 8
電壓 - 電源 (Vcc/Vdd)： 2.7 V ~ 3.6 V
數(shù)據(jù)轉(zhuǎn)換器： A/D 10x16b; D/A 1x12b，2x16b
振蕩器型： 內(nèi)部
工作溫度： -40°C ~ 125°C
封裝/外殼： 52-QFP
包裝： 托盤
Data Sheet
ADuC845/ADuC847/ADuC848
Rev. C | Page 83 of 108
Timer 3 Generated Baud Rates
The high integer dividers in a UART block mean that high
speed baud rates are not always possible. Also, generating baud
rates requires the exclusive use of a timer, rendering it unusable
for other applications when the UART is required. To address
this problem, the ADuC845/ADuC847/ADuC848 have 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 bps to 393216 bps 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 61.
÷ (1 + T3FD/64)
T3 Rx/Tx
CLOCK
CORE
CLK
T3EN
Rx CLOCK
Tx CLOCK
TIMER 1/TIMER 2
Rx CLOCK
FRACTIONAL
DIVIDER
0
1
TIMER 1/TIMER 2
Tx CLOCK
÷ 16
÷ 2DIV
04741-058
Figure 61. Timer 3, UART Baud Rate
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 to set up the binary
divider (DIV).
The appropriate value to write to the DIV2-1-0 bits can be
calculated using the following formula where fCORE is defined in
PLLCON SFR. Note that the DIV value must be rounded down.
DIV =
)
2
(
log
16
log
×
Rate
Baud
Frequency
Clock
Core
T3FD is the fractional divider ratio required to achieve the
required baud rate. The appropriate value for T3FD can be
calculated with the following formula:
T3FD =
Rate
Baud
Frequency
Clock
Core
DIV
×
1
2
64
Note that T3FD should be rounded to the nearest integer. Once
the values for DIV and T3FD are calculated, the actual baud
rate can be calculated with the following formula:
Actual Baud Rate =
)
64
(
2
1
+
×
T3FD
Frequency
Clock
Core
DIV
For example, to get a baud rate of 9600 while operating at a core
clock frequency of 1.5725 MHz, that is, CD = 3,
DIV = log(1572500/(16 × 9600))/log2 = 3.35 = 3
Note that the DIV result is rounded down.
T3FD = (2 × 1572500)/(231 × 9600) 64 = 18 = 12H
Therefore, the actual baud rate is 9588 bps, which gives an error
of 0.12%.
The T3CON and T3FD registers are used to control Timer 3.
T3CON – Timer 3 Control Register
SFR Address:
9EH
Power-On Default:
00H
Bit Addressable:
No
Table 55. T3CON SFR Bit Designations
Bit No.
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.
6
Not Implemented. Write Don’t Care.
5
Not Implemented. Write Don’t Care.
4
Not Implemented. Write Don’t Care.
3
Not Implemented. Write Don’t Care.
2, 1, 0
DIV2, DIV1, DIV0
Binary Divider
DIV2
DIV1
DIV0
0
Binary Divider 0. See Table 57.
0
1
Binary Divider 1. See Table 57.
0
1
0
Binary Divider 2. See Table 57.
0
1
Binary Divider 3. See Table 57.
1
0
Binary Divider 4. See Table 57.
1
0
1
Binary Divider 5. See Table 57.
1
0
Binary Divider 6. See Table 57.
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