UART_IE
HCLR4(sc, UART_IE, UART_IE_TXWM);
HSET4(sc, UART_IE, UART_IE_TXWM);
HSET4(sc, UART_IE, UART_IE_RXWM);
HCLR4(sc, UART_IE, UART_IE_TXWM | UART_IE_RXWM);