6.2.3 Write Lock

The Write Lock option provides the ability to render individual bytes within a user zone read-only by restricting all write operations to it. It operates at the 8-byte page level whereby the lowest addressed byte of the page serves as the write access control byte for that page. Table 6-2 shows the use of Write Lock for data at addresses $080 to $087. The byte at $080 controls write access to bytes from $080 to $087.

The Write Lock option also applies to the access control byte for each page by writing its least significant (rightmost) bit to Logic 0. Moreover, only logic modifications from Logic 1 to Logic 0 of the access control byte are permissible. Write Lock is available for any user zone and is selectable by configuring appropriate access registers. Furthermore, configuring a user zone with the Write Lock option restricts writing to that zone to a byte at a time. Attempts to write several bytes within a command results in writing only the first byte.