Z8F021ASH020SC datasheet(161/276 Pages) ZILOG

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PS022815-0206

Flash Memory

Z8 Encore! XP® 4K Series

Product Specification

142

sector can no longer be written or erased. After a bit of the Sector Protect Register has

been set, it can not be cleared except by powering down the device.

Byte Programming

The Flash Memory is enabled for byte programming after unlocking the Flash Controller

and successfully enabling either Mass Erase or Page Erase. When the Flash Controller is

unlocked and Mass Erase is successfully completed, all Program Memory locations are

available for byte programming. In contrast, when the Flash Controller is unlocked and

Page Erase is successfully completed, only the locations of the selected page are available

for byte programming. An erased Flash byte contains all 1’s (FFH). The programming

operation can only be used to change bits from 1 to 0. To change a Flash bit (or multiple

bits) from 0 to 1 requires execution of either the Page Erase or Mass Erase commands.

Byte Programming can be accomplished using the On-Chip Debugger's Write Memory

command or eZ8 CPU execution of the LDC or LDCI instructions. Refer to the eZ8 CPU

User Manual (available for download at www.zilog.com)for a description of the LDC and

LDCI instructions. While the Flash Controller programs the Flash memory, the eZ8 CPU

idles but the system clock and on-chip peripherals continue to operate. To exit program-

ming mode and lock the Flash, write any value to the Flash Control register, except the

Mass Erase or Page Erase commands.

The byte at each address of the Flash memory cannot be programmed (any bits written

to 0) more than twice before an erase cycle occurs. Doing so may result in corrupted data

at the target byte.

Page Erase

The Flash memory can be erased one page (512 bytes) at a time. Page Erasing the Flash

memory sets all bytes in that page to the value FFH. The Flash Page Select register identi-

fies the page to be erased. Only a page residing in an unprotected sector can be erased.

With the Flash Controller unlocked and the active page set, writing the value 95h to the

Flash Control register initiates the Page Erase operation. While the Flash Controller exe-

cutes the Page Erase operation, the eZ8 CPU idles but the system clock and on-chip

peripherals continue to operate. The eZ8 CPU resumes operation after the Page Erase

operation completes. If the Page Erase operation is performed using the On-Chip Debug-

ger, poll the Flash Status register to determine when the Page Erase operation is complete.

When the Page Erase is complete, the Flash Controller returns to its locked state.

Mass Erase

The Flash memory can also be Mass Erased using the Flash Controller, but only by using

the On-Chip Debugger. Mass Erasing the Flash memory sets all bytes to the value FFH.

With the Flash Controller unlocked and the Mass Erase successfully enabled, writing the

Caution:

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