z8f1621 ZiLOG Semiconductor, z8f1621 Datasheet - Page 197

• Manufacturer Part Number: z8f1621
• Description: High Performance 8-bit Microcontrollers
• Manufacturer: ZiLOG Semiconductor

®
Z8 Encore! XP
F64XX Series
Product Specification
183
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. Re-write 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
programmed or erased. Once 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 register
with 5EH. Once 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 de-selects the
Flash Sector Protect register and re-enables access to the Page Select register.
Follow the steps below to setup the Flash Sector Protect register from user code:
1. Write 00H to the Flash Control register to reset the Flash Controller.
2. Write 5EH to the Flash Control register to select the Flash Sector Protect register.
3. Read and/or write the Flash Sector Protect register which is now at Register File
address FF9H.
4. Write 00H to the Flash Control register to return the Flash Controller to its reset state.
Flash Write Protection Option Bit
The Flash Write Protect option bit can be enabled to block all program and erase opera-
tions from user code. For more information, see
Option Bits
on page 191.
Byte Programming
When the Flash Controller is unlocked, writes to Flash Memory from user code will pro-
gram a byte into the Flash if the address is located in the unlocked page. An erased Flash
byte contains all ones (
). The programming operation can only be used to change bits
FFH
from one to zero. To change a Flash bit (or multiple bits) from zero to one requires a Page
Erase or Mass Erase operation.
Byte Programming can be accomplished using the eZ8 CPU’s LDC or LDCI instructions.
™
For a description of the LDC and LDCI instructions, refer to eZ8
CPU Core User Man-
ual (UM0128).
PS019921-0308
Flash Memory