3 ms·
>a pullup capacitor on the UART VCC Why was it there? What were its two ends connected to? I have heard of pull-up resistors and decoupling capacitors but not
by rramadass 4y ago
>a pullup capacitor on the UART VCC
Why was it there? What were its two ends connected to? I have heard of pull-up resistors and decoupling capacitors but not a pull-up capacitor.
- unwind 4y agoMy guess would be that it was instead of the direct connection to power that was needed (since a bypass, i.e. a direct connection to power) fixed it. That would be a rather significant schematic and/or board design error though, which sounds fantastic, but sometimes things happen.
- rramadass 4y agoNot clear what you mean ? The pull-up capacitor was connected between VCC and what? AFAIK, a decoupling capacitor is used between VCC and ground and hence my confusion.
- gumby 4y agoInstead of a pull-up resistor between the uart vcc pin and vcc, there was an electrolytic cap. That is why I put “capacitor” in italics — I was trying to emphasize how nonsensical it was. To the DC power to the chip the cap was of course an open circuit and thus by shorting it out I powered the chip up. I assume it was a fumblefinger on the CAD system.
- Gibbon1 4y agoI'm assuming a bypass cap connected between vcc and one of the UART RX/TX lines.