EPROM Eraser not erasing New EPROM

[Donald Whisnant]

> Date: Fri, 14 Apr 2000 16:49:47 PDT
> From: "mike mager" <mikemager at hotmail.com>
> Subject: Re: EPROM Eraser not erasing New EPROM
> 
> Can you _prove_ that you are really reading the memory?  A typical 'memory
> check' algorythm would do it (and you can do it 'by hand');  an ultra-simple
> first stage would be:
> 
> Program(!) each location:
> 
> 00000000 with 00000000 (00)
> 00000001 with 00000001 (01)
> .
> .
> .
> 11111111 with 11111111 (FF)
> 
> . . . and so on;  you can enter the data by hand (yick!), or write a trivial
> program to create it.  There are more stages, inverse patterns, combination
> patterns, and stuff, but can you really read it/write it at all?
> 

Mike,

Using 00 = 00, 01 = 01, etc isn't a good idea...  If it is a multiplexed
address/data bus (as I'm assuming it is), there is often enough
capacitance on the address lines that you'll read out the low-word of
the address as "data" if the ROM (or any other memory device) isn't
getting enabled...  In other words, pull the rom and read address 0000
and you'll probably get 00, read 0001 and you'll probably get 01,
etc...  Instead, use a walking bit pattern: 01, 02, 04, 08, 10, 20, 40,
80, 01, 02, 05, 0A, 15, 2A, 55, AA, etc...  This will test for shorted
adjacent data bits as well as verify reading...

Donald
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