xe8802 Semtech Corporation, xe8802 Datasheet - Page 93

• Manufacturer Part Number: xe8802
• Description: Data Acquisition Soc With 16+10 Bit Zoomingadc? Embedded Risc Controller And Lcd Driver
• Manufacturer: Semtech Corporation

In order to obtain a correct baud rate, the RC oscillator or external clock frequency have to be set to one of the
frequencies given in the table below. The precision of the obtained baud rate is directly proportional to the
frequency deviation of the used clock source with respect to the values in the table below.
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 14-9.
RC frequency (Hz)
External clock freq. (Hz)
Note 1 : Although not documented here, the coding of the baud rate used in the circuits XE8801, XE8803 and
XE8805 can also be used.
Note 2 : 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.
14.7 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 bits as shown in Table 14-10.
© Semtech 2006
UartRcSel
000
010
UartBR
111
110
101
100
011
010
001
000
001
000
RC oscillator (Hz)
2’457’600
1’228’800
614’400
307’200
153’600
76’800
Frequency selection for correct Uart baud rates
2457600
4915200
153600
76800
38400
19200
9600
4800
2400
1200
600
300
Table 14-9: Uart baud rate with RC clock or external clock
Table 14-10: Uart baud rate with Xtal clock
1228800
2457600
76800
38400
19200
XE8802 Sensing Machine Data Acquisition MCU
9600
4800
2400
1200
600
300
-
Xtal freq. (Hz)
UartBR
011
010
001
000
Table 14-9a
1228800
614400
38400
19200
9600
4800
2400
1200
14-4
600
300
-
-
with ZoomingADC™ and LCD driver
External clock (Hz)
307200
614400
32768
19200
2400
1200
9600
4800
2400
1200
600
300
600
300
-
-
-
4’915’200
2’457’600
1’228’800
614’400
307’200
153’600
153600
307200
9600
4800
2400
1200
600
300
-
-
-
-
153600
76800
4800
2400
1200
600
300
-
-
-
-
-
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