SPI issues

average joe

EDIT... I'm beginning to suspect something other than what I thought going on....

I keep frying SPI FLASH and SRAM chips with no explanation (that I can logically see). With the chips removed from the board, I'm getting between 0.5v to about 1.5v from the pin (connected to DO of SPI chips) with the propeller held in reset. There is no pull-up on this pin, and no other possible source of current than the propeller. I've also checked a few other (unconnected) pins and I'm receiving the same results of between 0.5v to 1.5v. If I put a working spi chip (breadboard tested) on the board, when removed it no longer works. On my breadboard setup, I get about 0.3v from a high impedance pin. Other than the voltage issue, the rest of the chip appears to work correctly. So my question is does it sound like a bad chip? Or could there be something I'm missing?

Peter Jakacki

average joe wrote: »

I've been fighting with an issue for a while and I'm beginning to suspect a bad propeller.

I keep frying SPI FLASH and SRAM chips with no explanation (that I can logically see). With the chips removed from the board, I'm getting between 0.5v to about 1.5v from the pin (connected to DO of SPI chips) with the propeller held in reset. There is no pull-up on this pin, and no other possible source of current than the propeller. I've also checked a few other (unconnected) pins and I'm receiving the same results of between 0.5v to 1.5v. If I put a working spi chip (breadboard tested) on the board, when removed it no longer works. On my breadboard setup, I get about 0.3v from a high impedance pin. Other than the voltage issue, the rest of the chip appears to work correctly. So my question is does it sound like a bad chip? Or could there be something I'm missing?

Voltage and current are related yet different, you are measuring voltage with a high-impedance multimeter, so it presents no real load and it only reports the DC average. Place the probe on any bit of stray wire and you will read a "voltage" of some kind. Try it with a scope and you will see things better, what it really is, all kinds of hum and other EM energy that clutters the ether.

Now that was one thing but your dead chips are another. Don't just tell us it no longer works, you said there could be something you are missing but we are missing everything, what it looks like, the schematic etc. But feed us this info and I'm sure one of us will come up with the answer.

jmg

Good meters have high impedances on the lower ranges, so it is better to add a 10k pullup/pulldown and measure the 10k voltage in each case.
That will give you the actual pin-leakage current. 1uA = 10mV

average joe

Thanks for the response guys. I wish I could share more info but unfortunately I'm waiting for approval to disclose partial layout. I can show a partial schematic. The SPI pins are not used anywhere else. I will be testing with my DSOnano, had to let it charge last night.

(edit)

I've run some testing with the scope ( Input impedance: >500KΩ) and have seen a single spike of 2.4v for ~200uS. I've only seen this spike once, can't seem to replicate it. I'll keep trying and see if I can track it down. From earlier Logic Analyzer testing, the DO pin never goes low (LA has internal pull-ups).


(aedit)

After some more examination, it appears to be a clock issue! My breadboard test was running on RCfast. As soon as I switched to external (80Mhz) propeller clock, the breadboard test is failing the same way the in-circuit test was failing. Still doesn't explain the dead chips, although I think that's a separate issue.