Re: [hardware][avr] Один UART - два переферийных устройства

Всё уже придумано до нас (ц)

Читаем ман по атмеге:

Multi-processor Communication Mode

Setting the Multi-processor Communication Mode (MPCM) bit in UCSRA enables a fil- tering function of incoming frames received by the USART Receiver. Frames that do not contain address information will be ignored and not put into the receive buffer. This effectively reduces the number of incoming frames that has to be handled by the CPU, in a system with multiple MCUs that communicate via the same serial bus.