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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
@user49986 there's a 40k pull-up (to 3.3v) inside the chip (which is enabled by default). With the external 47k pull-down it manages to bias the voltage to 1.8v (ish).
It has the nice effect of pulling the signal to 3.3v (the 'idle' state for the UART) when the cable is not connected. If you were using some other non-espruino device that didn't have switchable internal resistors then you'd have to add an external pullup.
@user50001 I'd wondered about that. The problem is that the screen only really refreshes at max 60Hz, so it would be very slow to transfer data. This solution actually works without needing any special software on the host you're communicating with. As long as the UART is set to 9600 baud it'll work.
@DrAzzy I'm not sure - I don't seem to have problems here.