strange problem with flash, M29F040B

I doubt the flash chip itself is doing that, unless perhaps it got physically damaged (wrong voltage, ESD).

How do you know your logic is OK ?

Are there any other devices on the same bus ?

Try disconnecting the CS# or OE# pin, and see if the problem persists. If you don't get well defined data, hold a pull-up resistor on a data line while you read.

If the flash is socketed, take it out, and program it externally, and see what you read back.

Are you sure there is no address space conflict? Put your software in a continuous loop reading 0x300-0x30F. Scope the address and select lines on the flash chip.

Arlet schrieb: ...

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Unfortunately the flash is a soldered plcc device. There is a to strong pattern (error in every block) to not beleave that it comes from that flash. CS is only attached to that flash device.

Thx, Adib

Looks like you will need to change the flash. Is there room to fit a SMD PLCC socket ?

Before you replace the flash, pgm and verify one with a test pattern. A pattern we use here, is a decrementing counter, that shifts on every 256 byte page ( XOR with upper Adr byte)

- that makes every page unique, and the direction is 'opposite' the address, but it is a very simple pattern to verify.

-jg

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ok. first thing tomorrow I will try that and report. This issue costed my hours and hours. A flash I can program externaly.

thx, Adib.

Also clean-up the pins on the one you remove [ if it is still intact :) ], and read that in the programmer, just to check it really does have some 55H, then try and PGM those stuck locations.

-jg

...

... The flash is ok. I can measure something on the data bus now. Still I read 55 on that specific addresses :-? Still 3 more chips connected to the data bus. Removing the whole chip was even simpler than disconnect a single pin that I was focused on :-)

Thx, for pointing me in right direction.

Adib.

Looks like a marginal timing issue or glitch on write to the flash. Some combination of address and data bits that are close to or outside device tolerance.

A logic analyser is probably the only way to debug this. You can write a test program to generate signals at or around the address where the error occurs and verify that there are no glitches and that timing is within data sheet values. In particular. check data setup and hold times. You could also try decoupling caps around the flash and associated devices to see if this makes any difference...

Chris