Boot issue with 5v on inputs
Graham Stabler
Posts: 2,510
Hi all,
It's been a long time.
I'm using a FLiP module along with some external solid state relays for an automation project. These switch 5v to the inputs of the propeller, I use a 10k pull down resistors and a 300 ohm resistor in series to protect the input.
I find that if I boot the system using the same 5v supply that provides these signals that the propeller does not boot, no issue with the power LED though. If I boot from the USB and then power the system with the 5v there is no problem. Likewise if I remove the solid state relays from their holders I don't have an issue so it seems like it does not like having 5v on the pins on boot.
This is on site being used in a system so I've no had a lot of time to debug but will be working on it tomorrow.
Cheers,
Graham
Comments
Graham,
It sounds like the 5V inputs are leeching power through the inputs to the Propeller chip, probably via protection diodes. This can happen on other microcontrollers and chips, like the FT232. Best to prevent 5V input voltage when the MCU is not powered, if you can help it.
It's the interlock system so if they open up the door and press the e-stop button then that would work but not what I was hoping for.
I saw that something like this was a problem on the protoboards but they have now added 10k resistors between the FTDI and propeller to prevent it.
Cheers,
Graham
Looks like going to 1k in series might be worth a try.
Graham,
If you can post just the relevant portion of the schematic for these inputs, there may be another way to do it. I mean, if the Propeller isn't powered, it can't take any action based on the inputs anyway. But of course, without the schematic I don't have any context for what you're trying to do. Might be a way around it though.
Depending on how the series / pull-down resistors are configured, you may also be creating a voltage divider.
The Flip is using the newish FT231X chip which I believe are supposed to not have the power leaching reboot problem.
But, I think 300 Ohm series resistor is too low. Think need 2k or more...
Why that makes it not boot though, I don't know...
Maybe I'd try flashing with the boot code in RC fast mode and see if it's the oscillator circuit that is broke...
Rayman,
I didn't mean to confuse the issue by bringing up the old FT232 problem. I was relating it to what is happening now. In this case, the 5V is going to an input pin. I believe that, if it was a 3.3V signal, this probably would not be happening, though, without a schematic, I can't be sure of anything.
The usb powers the regulator for the 3.3volts. I use opto isolators for inputs and outputs. Run your flip by it self to make sure you haven’t blown any pins.