Pull-up (and pull-down) revisited

Use this forum to chat about hardware specific topics for the ESP8266 (peripherals, memory, clocks, JTAG, programming)
 Reply

User avatar

Re: Pull-up (and pull-down) revisited

By eriksl
- Sat Mar 19, 2016 10:16 am #43556 All inputs are clear, no internal pull-ups. I know that because I write the firmware myself ;)

I don't like the internal pull-ups because:

- they're not real pull-ups, they're current sources (see explanation from a.o. ATmel in their docs)
- they're too weak to make a real difference

Also, it's not clear whether enabling the internal pull up on a pin is honoured when the pin is routed to the UART. I actually doubt it.
User avatar

Re: Pull-up (and pull-down) revisited

By AdrianM
- Sat Mar 19, 2016 10:58 am #43562
eriksl wrote:All inputs are clear, no internal pull-ups. I know that because I write the firmware myself ;)

I don't like the internal pull-ups because:

- they're not real pull-ups, they're current sources (see explanation from a.o. ATmel in their docs)
- they're too weak to make a real difference

Also, it's not clear whether enabling the internal pull up on a pin is honoured when the pin is routed to the UART. I actually doubt it.


Yet you seemed to be surprised that you needed to add an external pull-up on RXD. Very confusing (but then again I'm easily confused).

But serioulsy, I really would like to know why you think current sources are not effective as pull-ups and why ~27K equivalent is too weak. I couldn't work out what ATmel doc you were referencing. 50uA is about as much as I've ever needed to "establish" a logic level at a MOS input in a noisy RF environment. After all, it's just fighting electric fields that might otherwise put charge on the MOS gates.
User avatar

Re: Pull-up (and pull-down) revisited

By RichardS
- Sat Mar 19, 2016 1:15 pm #43571
martinayotte wrote:
eriksl wrote:The GPIO1 and GPIO3 where high-impedance though (of course, if you think of it, nothing connected). I started with a pull-down. I used 1k for a strong pull but not too strong to damage the driver (1k = 3.3 mA). This made the pin going down all of the time, rendering the UART unusable and also made the esp not boot up. Then changed the resistors to pull-up and voilà, all working again.

Did you tried to pulled up RX only while leaving TX floating ?
Because it could be that RX with LOW state is interpreted as Break signal ...


Can you try what Martin is saying I would like to know.... just pull up RX

RichardS
 Reply
Return to Hardware Specific