ZUSBOPTSC01ZACG datasheet(167/282 Pages) ZILOG

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PS022827-1212

P R E L I M I N A R Y

Operation

Z8 Encore! XP® F082A Series

Product Specification

150

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 Regis-

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

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

active. See Figure 22 on page 148 for details.

After unlocking a specific page, you 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, you 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! XP devices are divided into maximum number of 8 sectors. A sector is 1/8

of the total Flash memory size unless this value is smaller than the page size – in which

case, the sector and page sizes are equal. On Z8 Encore! F082A Series devices, the sector

size is varied according to the Flash memory configuration shown in Table 78 on page

146.

The Flash Sector Protect Register can be configured to prevent sectors from being pro-

grammed or erased. After a sector is protected, it cannot be unprotected by user code. The

Flash Sector Protect Register is cleared after reset, and any previously-written protection

values are lost. User code must write this register in their initialization routine if they pre-

fer to enable sector protection.

The Flash Sector Protect Register shares its Register File address with the Page Select

Table 79. Flash Code Protection Using the Flash Option Bits

FWP Flash Code Protection Description

Programming and erasing disabled for all of Flash Program Mem-

ory. 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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