Hi all
I though a few here might find this interesting.
I'm currently working on a project using an Atmel ATMEGA324P/V (picopower variant), the board has no RS-232, only RS-485 (MAX487). I included a header for TTL serial interface. Was using this header to run some diagnostics on my firmware via a USB - TTL (5v) serial cable (Don you know the ones). I was more than a little surprised when the program actually started running and returning values with the power supply completely disconnected.
Only GND, RX & TX connected on the cable
So through the hardware UART on the AVR I was having it powered and run at the correct speed (seemingly) using external crystal osc. to deliver a perfect data stream at 19200 baud.
Measured Vcc @ 1.7v (BOD was not set)
It took me a while to realise what was happening since it was initially after I'd had the thing running and disconnected power and thought there was some magical smoke & mirrors buffer in Windows doing some crazy stuff.
Anyone come across this before?
Regards James
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