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[avr-chat] EEAR8 on tiny devices with EEPROM <= 256B

From: Ruud Vlaming
Subject: [avr-chat] EEAR8 on tiny devices with EEPROM <= 256B
Date: Wed, 2 Sep 2009 12:05:29 +0200
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The attiny24/44 have so small an EEPROM that it can be addressed
by one byte, as the manual clearly states, (page 20). Bit EEAR8
is reserved for the ATtiny24/44, so effectively you do not
need EEARH at all for these devices. And it will read zero allways.

A comparable situation exists for the ATtiny25/45 and ATtiny261/461.
These devices also have one byte addressable EEPROMs, but the manuals
suggest (page 20, resp 21) that EEARH must be written nevertheless.

A quick test with the 261/861 seems to indicate that they behave
as if the bit is indeed reserved on the 261, reading of EEAR8
returns a zero, even if a one was written. For the 861 the EEAR8
bit behaves as a memory. But, it could be that this situation
is device specific. In other words, it would not contradict the
current version of the manual, if there are 261 devices out their
that return a one when reading EEAR8. It would not be in line
with their usual policy on reserved bits however.

I did not test all devices, but my primilairy conclusion would
be that the manuals on 261/461/861 and 25/45/85 need to be


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