XE8806A SEMTECH [Semtech Corporation], XE8806A Datasheet - Page 112

• Manufacturer Part Number: XE8806A
• Description: Ultra Low-Power Low-Voltage
• Manufacturer: SEMTECH [Semtech Corporation]

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%.
15.8 Function description
15.8.1
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 15.5). The bits UartSelRc and UartBR select the
baud rate (see chapter 15.5).
The bits UartEnRx and UartEnTx are used to enable or disable the reception and transmission.
The word length (7 or 8 data bits) can be chosen with UartWL. A parity bit is added during transmission or checked
during reception if UartPE is set. The parity mode (odd or even) can be chosen with UartPM.
Setting the bits UartXRx and UartXTx inverts the Rx respectively Tx signals.
The bit UartEcho is used to send the received data automatically back. The transmission function becomes then:
Tx = Rx XOR UartXRx XOR UartXTx.
15.8.2
In order to send data, the transmitter has to be enabled by setting the bit UartEnTx. Data to be sent have to be
written to the register RegUartTx. The bit UartTxFull in RegUartTxSta then goes to 1, indicating to the transmitter
that a new word is available. As soon as the transmitter has finished sending the previous word, it then loads the
contents of the register RegUartTx to an internal shift register and clears the UartTxFull bit. An interrupt is
generated on Irq_uart_Tx at the falling edge of the UartTxFull bit. The bit UartTxBusy in RegUartTxSta shows
that the transmitter is busy transmitting a word.
A timing diagram is shown in Figure 15-1. Data is sent LSB first.
New data should be written to the register RegUartTx only while UartTxBusy is 0, otherwise data will be lost.
© Semtech 2006
Configuration bits
Transmission
15-5
XE8806A/XE8807A
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