SX8801IRXXMLTRT View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SX8801IRXXMLTRT' PDF : 135 Pages View PDF
XE8801A – SX8801R
Frequency selection for correct Uart
baud rate with RC oscillator (Hz)
2’457’600
1’843’200
1’228’800
614’400
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)
UartRcSel
111
UartBR
110
101
100
2’457’600
010
Not possible
1’228’800
001
38400
19200
9600
4800
614’400
000
Table 14-8: Uart baud rate with RC clock
1’843’200
000
115200
57600
28800
14400
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 Uart on the crystal oscillator
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.
Xtal freq. (Hz) UartRcSel
32768
001
UartBR
011
010
001
000
Baud rate
2400
1200
600
300
Table 14-9: Uart baud rate with Xtal clock
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 Configuration bits
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 bit UartEnTx is used to enable or disable the transmission.
© Semtech 2005
14-4
www.semtech.com
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