Fluke Addressing Problem

[invadarr]

Can anyone please help with a fluke problem I have?

I have done a ramshort test on a board @ loc 4000-4FFF.

I get an error which says Ram DCD error @ Loc 4022 bit 8.

I then did a write @ 4122- FF.

I then did a write @ 4022- AA.

I then did a Read @ 4122 ans=FF.

I then did a Read @ 4022 ans=AA.

The problem is as I see it, is that if the fluke see's 4022 and 4122 as the same address

then the 4122 address should read as AA. indicating the dcd error.

Can any one explain what may be happening here (am I doing something wrong?)

I have tried this proceedure many times and the result is always the same on this board.

When I have carried out dcd errors in the past with the Fluke it has always been posible to find the fault

as one can determine that the fluke see's the two addresses as being one address due to an error on the board,

useualy because the Bit in question is being held High.

any help would be most appreciated

Thanks Pete (invadar)

 

[Macro]

ram test writes a value to each location based upon the address, if it reads back a different value it goes with the decode error (since it got the data that was meant to be elsewhere)

so, it could mean that bit 8 is tied to another signal - if it were a data line then whether you received an error or not would depend on whether you were trying to drive the data line at a different value to the address line.

so now try writing 4022 with FF and 4122 with 00 - but of course this only assumes that it is tied with a data line

I have often found DCD errors that are internal to the chip (especially on 2114's) - so sometimes swopping the chip can fix the fault.