SRAM 'OE' pin query

Not necessarily. The OE pin is usually "active low" meaning that an external circuit must drive the pin to a low state to enable the chips outputs. It may have a weak internal pullup resistor that you see as a voltage present on the pin. Try grounding the pin and see if your circuit starts working.

I see, thanks. Well I tried grounding the pin and that pulled it low but made no difference.

I should also have mentioned that this particular chip gets rather hot compared to the others that are the same as it on the PCB.

Cheers

What does the data sheet say about this pin?

Tying it low may mean that it's trying to drive its outputs at inappropriate times. Are there chip select and read/write strobes that you're also controlling?

FWIW, the only 41256 parts that I could locate datasheets for were all dynamic RAMS and none had OE pins.

--
Rich Webb   Norfolk, VA

If I could understand it all I'd tell you. :-)

I got it from:

Part no: 3005392

Just key in that number and the search result will come back.

Then click on the Orange order code to the left, and on the next page click on the datasheet (PDF format).

Not sure I'm afraid - I don't have any schems for this board.

I do know though that this (and another RAM) is being driven by the output of a 7414 (Hex schmitt inverter - pin 10 (this 7414 is also connected to an oscillator via another pin). In fact, it was looking at this 7414 with my logic probe that highlighted something being wrong - the probe would NOT light up high or low with the probe on pin

10 of the 7414, but on lifting pin 10 it then went low as expected.

Re-connected pin 10 of the 7414 and traced it to pin 22 of the aforementioned RAM and found that lifting pin 22 (OE) of the RAM also caused pin 10 of the 7414 to go low (as expected) and that pin 22 of the RAM, when lifted, was still high (which seemed unusual, especially when it's also noted that this particular RAM is getting noticeably hotter than the others of the same type).

Curious.

Thanks

Ahhh... It's an AS7C256. Different critter.

It's always possible that it's faulty. CMOS is sensitive to static discharge damage. I'd guess that even in the UK it gets a *bit* dry in the winter months... ;-)

Otherwise, CMOS typically won't dissipate energy unless it's switching, so perhaps it's more active than it should be. Are all of the address and control lines connected to a driver or pulled high? Also, there's a note that "CE or WE must be High during address transitions."

If you don't have an o-scope or logic analyzer handy, consider one of the gizmos from

I've had one of their 8-channel analyzers since they first came out and still carry it with me in my notebook PC bag. Eight (even sixteen) channels aren't enough to see

*everything* but are enough to get a better idea of what's happening.

--
Rich Webb   Norfolk, VA

Ah, good. :)

Well, *sometimes* ............ :-)

From what I recall, I think they're all high.

Hmmm, I see. Worth swapping it out though do you think?

Thanks for the tip, will take a look.

Happy Christmas. :-)