On Thu, 10 Aug 2006 07:23:52 +1000, you wrote:

>At 07:04 AM 10/08/2006, you wrote:
>>Add in their reputation (as I've heard) for discontinuing parts at an
>>above-average rate,
>
>True, but I have found that they seem to always have a
>pin and mostly code compatible (very small changes if any)
>chip which is cheaper than the one it replaces and it has more
>features. 

..and just for fun they throw in the occasional extremely subtle change that takes forever to
find...

Original product used 90S4414. When this went obsolete, changed to 90S8515. Then this went obsolete,
changed to tiny8515, which exhibited  wierd behaviour similar to eeprom corruption, but the whole
eeprom appeared to be getting lost.

After a week or so of head-scratching, figured it out : 
90S4414 has 256 bytes eeprom, so no high-order address bit.
90S8515 has 512 bytes eeprom, but high-order address bit initialises to 0 on reset.
Mega8515 does not initalise high-order address bit on reset, so random eeprom page selected....

One thing that made this harder to figure out was our product had a 2200uf cap across the 5V rail to
keep a couple of  RC servos happy. This meant that  you could leave it powered off for an hour or
two after programming & it would coem back on  fine, A few hours longer (i.e. after shipping to
customer) and it would fail.

 


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