I have another question.

[Ian Rogers]

I have a board in for repair, actually several. All have the same issue. As you know I work mainly digital.

We have an 8051 from DS its an 89c450. and its has no SPI but has a software one.. I do not have the source so the software isn't viewable.

We have a loadcell connected to an amp then into an SPI MCP3201 12bit ADC.. The SDI in goes up to the MCU but via a schmitt hex buffer 74hc14 On the one side of the hex buffer is a weak pullup BUT!! either the MCP3201 SDI pin or the HEX input is shorted to ground.. Obviously some contention but I fail to see why..

I have asked them to place a 270 ohm resistor in the line but I cant see why it fails.
Any Ideas

 

[danadak]

schematic ?

 

[Ian Rogers]

Not mine so I can't show this But mcp3201 -> 74hc14 all digital signals 1&2 clk, 3&4 dout 5&6 CS.

 

[Nigel Goodwin]

From a practical point of view, outputs are far more likely to go S/C than inputs, so I'd suspect the MCP3201 has gone duff.

Could there possibly be large spikes coming through it's input?.

 

[Ian Rogers]

Maybe... I just found out that it is the same customer.. I suspect an external spike as the software SPI means the MCU will be floating and the input of the hex buffer is floating ( pulled up with a 10k ) so I cannot see any way other the external influence..

They will be handling the boards without protection... Just seems strange its the same track!!

I wonder if they are plugging in the ribbon cable wrong?

 

[ZipZapOuch]

Maybe... I just found out that it is the same customer.. I suspect an external spike as the software SPI means the MCU will be floating and the input of the hex buffer is floating ( pulled up with a 10k ) so I cannot see any way other the external influence..

They will be handling the boards without protection... Just seems strange its the same track!!

I wonder if they are plugging in the ribbon cable wrong?

If you are using FPC as ribbon cables, an upside down ribbon shouldn't be a problem if you have connectors that are either top OR bottom contacts only. You get into trouble if you have connectors with top AND bottom contacts.

 

[aliarifat794]

Check if the 74HC14 input pin (connected to SDI) is floating or properly driven. If it’s floating, it can cause unpredictable behavior.