XCore Exchange

Hi,

I am wondering if the GPIO pins on XS-2 series devices (e.g. XEF216-512-TQ128) include input clamping diodes? These are very common on CMOS inputs to provide basic ESD protection for the device. I don't see any mention of them in the datasheet, though.

The reason I ask is, I am wondering if it would be possible to simply interface a 5V TTL signal to an xCore input pin. TTL has a nominal "high" output voltage of 3.5V or less, but some TTL outputs include a weak pull-up resistor to 5V. If the xCore input includes a clamping diode to VDD (3v3), the TTL input could be interfaced directly. Clamping current from a high TTL output to VDD (3v3) would be 500µA or less (an appropriate series resistor can be used).

I realize that this is a "hackish" way of interfacing 5V TTL to a 3v3 CMOS input. I realize that I can possibly destroy the XMOS part. I just want to know if the XMOS GPIO inputs include calming diodes to VSS and VDD.

Thanks!

I would appreciate hearing an "official" answer, but FWIW:

With my xCore-200 explorerKIT, powered off, I used a DMM in "diode check" mode to measure between some the GPIO pins and VDD (3V3): it shows "open". Also, in ohmmeter mode, it shows high impedance (too high for my meter, anyway). So, if there were input clamp diodes to VDD, I would expect the DMM to show a voltage drop in diode mode, between 0.3 and 0.7V.

I'm guessing that clamp diodes are NOT present. I wonder how they implement ESD protection?...