Rainbow Electronics DS1855 - Manual (Page 5)

DS1855
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FBh – FCh Lock Bytes Writing to these two bytes allows the user to lock or unlock the
memory described in byte FAh.
LOCK: If memory location FBh is written to 56h and memory
location FCh is written to 25h, the device will enter lock mode.
Write protection will become active in the memory locations that
are specified in FAh.
UNLOCK: If memory location FBh is written to 67h and memory
location FCh is written to 36h, the device will be unlocked. Once
unlocked, the user can change the setting of memory location FAh
to affect the EEPROM write-protection.
The locking can be updated at any time as long as the upper
page is unlocked.
FD – FFh Reserved Reserved