In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Sparks-R-Fun wrote:

I have been tracking a troubling communication issue for many hours.  I have finally isolated the problem.  I think the solution should be easy yet it eludes me.  (This probably due to tired thinking on my part.)  What is wrong here?

I have an SX connected to a 3.3V device that is 5V tolerant.  Communication is via SPI commands.  The device is properly receiving commands from the SX.  However, the SX does not seem to be properly receiving data from the device.

To help troubleshoot this further I connected a Basic Stamp Logic Analyzer to the relevant SPI lines.  Indeed, the return data from the device does not seem to be correct.  Occasionally some of it seems to switch logic levels on the wrong clock edge.

From the perspective of the analyze it seems that the 3.3V device is not outputting the correct signaling sequence.  However, when I disconnect the SPI input line into the SX but leave the analyzer connected the return data appears fine!


The first question to address is this, "[B]Can the SX properly discern 3.3V logic signals?[/B]"  I am certain it can.

The second question then is, "[B]How do I prepare the SX to properly receive a 3.3V logic signal?[/B]"


I have tried to connect the SPI data output pin to an SX pin configured as a CMOS input with the pullup resistor disabled.


What am I missing?


 - Sparks

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