ADUC834: Is it possible to accidently write to security bits and prevent part entering download mode?

Document created by analog-archivist Employee on Feb 23, 2016
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The ADuC834 features security bits to restrict access to Flash/EE code and data
space. Can I
accidentally write to them in my code and prevent the part from entering serial
download mode?


The ADuC834 facilitates three modes of Flash/EE program memory security. These
modes can be
independently activated, giving different levels of security to your code as
described in the
ADuC834 datasheet (pg 38)
The security bits are read-only from user code and exist at byte address FFFEh.
They can be read
using the following piece of code.
MOV EADRH, #0FFh ; address the Sec Bits page
MOV ECON, #81H ; read byte command
The security bits can be only be set after parallel programming the ADuC834 or
directly after a
serial download by following the serial download protocol as described in
AN-1074. This
protocol is implemented in our Windows serial downloader (WSD) available as
part of the
QuickStart development system.