XE8805 SEMTECH [Semtech Corporation], XE8805 Datasheet - Page 77

• Manufacturer Part Number: XE8805
• Description: Data Acquisition MCU
• Manufacturer: SEMTECH [Semtech Corporation]

For each of these frequencies, the baud rate can be selected with the bits UartBR(2:0) in RegUartCtrl and
UartRcSel(2:0) in RegUartCmd as shown in Table 14-8
RC frequency (Hz)
Note: The precision of the baud rate is directly proportional to the frequency deviation of the used clock from the
ideal frequency given in the table. In order to increase the precision and stability of the RC oscillator, the DFLL
(digital frequency locked loop) can be used with the crystal oscillator as a reference.
14.5.2
In order to use the crystal oscillator as the clock source for the Uart, the bit SelXtal in RegUartCmd has to be set.
The crystal oscillator has to be enabled by setting the EnableXtal bit in RegSysClock. The baud rate selection is
done using the UartBR and UartRcSel bits as shown in Table 14-9.
Due to the odd ratio between the crystal oscillator frequency and the baud rate, the generated baud rate has a
systematic error of –2.48%.
14.6 Function description
14.6.1
The configuration bits of the Uart serial interface can be found in the registers RegUartCmd and RegUartCtrl.
The bit SelXtal is used to select the clock source (see chapter 14.5). The bits UartSelRc and UartBR select the
baud rate (see chapter 14.5).
The bits UartEnTx is used to enable or disable the transmission.
The bits UartEnRx1 and UartEnRx2 are used to enable or disable the reception. When one is set to 1, the
reception is enabled.
© Semtech 2006
UartBR
UartRcSel
Uart on the crystal oscillator
Configuration bits
111
110
101
100
Xtal freq. (Hz)
32768
Not possible
2’457’600
010
Frequency selection for correct Uart
baud rate with RC oscillator (Hz)
UartRcSel
001
Table 14-9: Uart baud rate with Xtal clock
Table 14-8: Uart baud rate with RC clock
2’457’600
1’843’200
1’228’800
614’400
1’228’800
38400
19200
001
9600
UartBR
011
010
001
000
14-4
4800
614’400
000
Baud rate
2400
1200
600
300
1’843’200
115200
57600
28800
14400
000
XE8805/05A
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