Z8F021ASH020SC datasheet(160/276 Pages) ZILOG

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PS022815-0206

Flash Memory

Z8 Encore! XP® 4K Series

Product Specification

141

Flash Code Protection Using the Flash Controller

At Reset, the Flash Controller locks to prevent accidental program or erasure of the Flash

memory. To program or erase the Flash memory, first write the Page Select Register with

the target page. Unlock the Flash Controller by making two consecutive writes to the

Flash Control register with the values 73H and 8CH, sequentially. The Page Select Register

must be rewritten with the target page. If the two Page Select writes do not match, the con-

troller reverts to a locked state. If the two writes match, the selected page becomes active.

See Figure 22 for details.

After unlocking a specific page, the user can enable either Page Program or Erase. Writing

the value 95H causes a Page Erase only if the active page resides in a sector that is not pro-

tected. Any other value written to the Flash Control register locks the Flash Controller.

Mass Erase is not allowed in the user code but only in through the Debug Port.

After unlocking a specific page, the user can also write to any byte on that page. After a

byte is written, the page remains unlocked, allowing for subsequent writes to other bytes

on the same page. Further writes to the Flash Control Register cause the active page to

revert to a locked state.

Sector Based Flash Protection

The final protection mechanism is implemented on a per-sector basis. The Flash memories

of Z8 Encore!® devices are divided into at most 8 sectors. A sector is 1/8 of the total size

of the Flash memory, unless this value is smaller than the page size, in which case the sec-

tor and page sizes are equal. On the Z8 Encore! XP® 4K Series devices, the sector size is

512 bytes, equal to the page size.

The Sector Protect Register controls the protection state of each Flash sector. This register

is shared with the Page Select Register. It is accessed by writing 73H followed by 5EH to

the Flash controller. The next write to the Flash Control Register targets the Sector Protect

The Sector Protect Register is initialized to 0 on reset, putting each sector into an unpro-

tected state. When a bit in the Sector Protect Register is written to 1, the corresponding

Table 80. Flash Code Protection Using the Flash Option Bits

FWP

Flash Code Protection Description

Programming and erasing disabled for all of Flash Program

Memory. In user code programming, Page Erase, and Mass Erase

are all disabled. Mass Erase is available through the On-Chip

Debugger.

Programming, Page Erase, and Mass Erase are enabled for all of

Flash Program Memory.

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