Fri Feb 4 13:12:17 EST 2011

3V input on 5V circuit.

I need to sniff a 3V SPI bus.  I only have 5V boards.  What's the
fastest way to interface?  For now it's only 3V -> 5V but near future
might need reverse too.

  * Build a 3V board.

  * Some inverter chip tricks?

It seems it's going to be far easier to just stick to 3V3 for the
sniffer.  PIC 3V3 pins are 5V tolerant.

See figure 26-3 in the 18LF2620 data sheet.  At 3V3 max speed is about
20 MHz.  It should be straightforward to modify the clock settings on
the 2620 to do this.

I tried with a 3V3 cable but didn't work.  Voltage measured 4.3V so
maybe I messed up the voltage regulator in the cable?  Check here [2].
The logic levels are 3.3 but the power is 5V.  Both 3V3 cables are the
same.  Why is that?  Ok, going from 4.7 -> 5.0 when using a powered

[1] entry://../electronics/20110204-131618
[2] http://www.ftdichip.com/Support/Documents/DataSheets/Cables/DS_TTL-232R_CABLES.pdf