The USART for one-wire communication on older megaAVR and tinyAVR devices will consume two pins. Also, it requires an external open-drain or open-collector circuit unless bit banging is used.
One-wire solutions on the new tinyAVR® 0- and 1-series and megaAVR® 0-series can be implemented with a lower bill of material (BOM) cost and with low CPU overhead, thanks to the updated USART peripheral. With the internal connection between RXD and TXD and Open-Drain mode on the pin, they introduce advantages that can be seen in the table below.
| Old USART Solution | New USART Solution | Bit Banging | |
|---|---|---|---|
| Interrupts | Active | Active | Disabled |
| Pins needed | 2 (TXD and RXD) | 1 (TXD) | 1 (any) |
| CPU Load | Low | Low | High |
| BOM | External components needed | No extra cost | No extra cost |
As can be seen from the table, the solution available on the new tinyAVR® 0- and 1-series and megaAVR® 0-series provides all the best aspects from the other solutions, except the fact that a dedicated TXD pin needs to be used instead of being able to use any pin, such as with bit banging. These devices are a great platform to develop a one-wire application on.