We're encountering a problem with an Am29F040B 512KB Flash memory chip. It works fine, except after A15 has been toggled quickly for about 300 msec, with chip select DEasserted and no accesses being made to chip. Then reads return $FF for several hundred msec, then slowly the bits return to what they should be. No other pin causes this. The odd thing is that during this period where reads don't work, I can do the special write sequence to enable Autoselect mode and successfully read the chip ID just fine. After doing this, I write $F0 to reset back to array read mode and get $FF again until the effect wears off. Programming a byte also seems to fail during this cool-off period.
Have tried adding extra bypass capacitors, and putting 1K and 10K resistors in series with A15. Supply voltage stays around 4.95 V when toggling A15 quickly, so it's not causing excessive current drain.
Any ideas on why just this one address pin would behave like that?
Have tried adding extra bypass capacitors, and putting 1K and 10K resistors in series with A15. Supply voltage stays around 4.95 V when toggling A15 quickly, so it's not causing excessive current drain.
Any ideas on why just this one address pin would behave like that?