34s flashing cable possible candidate?

[Dave Frederickson]

(06-25-2014 11:14 PM)cruff Wrote:  An older cable may be more likely to be a 5V version, which would damage anything using a lower voltage I/O.

Not necessarily true. Many devices have Low-Voltage TTL logic level pins, yet are 5V tolerant. From the Atmel datasheet:

Voltage on Input Pins
with Respect to Ground...... ..............................-0.3V to + 5.5V

So any circuitry (level-shifters) to ensure that the TTL signals are 3V is a waste.

Dave