That took me a while but I figured it out.
3.3V through the resistor provides a pullup.
When TX is low it pulls that down.
Mostly TX is high so there's not much wasted where a voltage divider would waste more.
That took me a while but I figured it out.
3.3V through the resistor provides a pullup.
When TX is low it pulls that down.
Mostly TX is high so there's not much wasted where a voltage divider would waste more.