USART FIFO global update register
| USART0RXUPDATESIZE | Writing 1 updates USART0 Rx FIFO size to match the USART0 RXSIZE. Must be done for all USARTs when any USART RXSIZE is changed. |
| USART1RXUPDATESIZE | Writing 1 updates USART1 Rx FIFO size to match the USART1 RXSIZE. Must be done for all USARTs when any USART RXSIZE is changed. |
| USART2RXUPDATESIZE | Writing 1 updates USART2 Rx FIFO size to match the USART2 RXSIZE. Must be done for all USARTs when any USART RXSIZE is changed. |
| USART3RXUPDATESIZE | Writing 1 updates USART3 Rx FIFO size to match the USART3 RXSIZE. Must be done for all USARTs when any USART RXSIZE is changed. |
| RESERVED | Reserved. Read value is undefined, only zero should be written. |
| USART0TXUPDATESIZE | Writing 1 updates USART0 Tx FIFO size to match the USART0 TXSIZE. Must be done for all USARTs when any USART TXSIZE is changed. |
| USART1TXUPDATESIZE | Writing 1 updates USART1 Tx FIFO size to match the USART1 TXSIZE. Must be done for all USARTs when any USART TXSIZE is changed. |
| USART2TXUPDATESIZE | Writing 1 updates USART2 Tx FIFO size to match the USART2 TXSIZE. Must be done for all USARTs when any USART TXSIZE is changed. |
| USART3TXUPDATESIZE | Writing 1 updates USART3 Tx FIFO size to match the USART3 TXSIZE. Must be done for all USARTs when any USART TXSIZE is changed. |
| RESERVED | Reserved. Read value is undefined, only zero should be written. |