FIFO configuration register for USART0
| RXSIZE | Configures the USART receive FIFO size. A zero values provides no System FIFO service for the related USART receiver. |
| TXSIZE | Configures the USART transmit FIFO size. A zero values provides no System FIFO service for the related USART transmitter. |
| RESERVED | Reserved. Read value is undefined, only zero should be written. |