Z8F4822AR020SG Datasheet, PDF (192/323 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F64xx Series
Product Specification
172
Flash Read Protection
The user code contained within Flash memory can be protected from external access. Pro-
gramming the Flash Read Protect option bit prevents reading of user code by the On-Chip
Debugger or by using the Flash Controller Bypass mode. For more information, see the
Option Bits chapter on page 180 and the On-Chip Debugger chapter on page 183.
Flash Write/Erase Protection
The Z8 Encore! XP F64xx Series provides several levels of protection against accidental
program and erasure of the Flash memory contents. This protection is provided by the
Flash Controller unlock mechanism, the Flash Sector Protect Register, and the Flash Write
Protect option bit.
Flash Controller Unlock Mechanism
At Reset, the Flash Controller locks to prevent accidental program or erasure of Flash
memory. To program or erase Flash memory, the Flash Controller must be unlocked. After
unlocking the Flash Controller, the Flash can be programmed or erased. Any value written
by user code to the Flash Control Register or Page Select Register out of sequence will
lock the Flash Controller.
Observe the following procedure to unlock the Flash Controller from user code:
1. Write 00H to the Flash Control Register to reset the Flash Controller.
2. Write the page to be programmed or erased to the Page Select Register.
3. Write the first unlock command 73H to the Flash Control Register.
4. Write the second unlock command 8CH to the Flash Control Register.
5. Rewrite the page written in Step 2 to the Page Select Register.
Flash Sector Protection
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 is lost. User code must write this register in their initialization routine if they want
to enable sector protection.
The Flash Sector Protect Register shares its Register File address with the Page Select
Register. The Flash Sector Protect Register is accessed by writing the Flash Control Regis-
ter with 5EH. After the Flash Sector Protect Register is selected, it can be accessed at the
Page Select Register address. When user code writes the Flash Sector Protect Register,
bits can only be set to 1. Thus, sectors can be protected, but not unprotected, via register
write operations. Writing a value other than 5EH to the Flash Control Register deselects
the Flash Sector Protect Register and reenables access to the Page Select Register.
PS019924-0113
PRELIMINARY
Operation