Z8F021ASH020SC datasheet(159/276 Pages) ZILOG

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PS022815-0206

Flash Memory

Z8 Encore! XP® 4K Series

Product Specification

140

Flash Operation Timing Using the Flash Frequency Registers

Before performing either a program or erase operation on Flash memory, the user must

first configure the Flash Frequency High and Low Byte registers. The Flash Frequency

registers allow programming and erasing of the Flash with system clock frequencies rang-

ing from 32 KHz (32768 Hz) through 20 MHz.

The Flash Frequency High and Low Byte registers combine to form a 16-bit value,

FFREQ

, to control timing for Flash program and erase operations. The 16-bit binary Flash

Frequency value must contain the system clock frequency (in KHz). This value is calcu-

lated using the following equation:

Flash programming and erasure are not supported for system clock frequencies below

32 KHz (32768 Hz) or above 20 MHz. The Flash Frequency High and Low Byte regis-

ters must be loaded with the correct value to ensure operation of the Z8 Encore! XP®

4K Series devices.

Flash Code Protection Against External Access

The user code contained within the Flash memory can be protected against external access

by the on-chip debugger. Programming the FRP Flash Option Bit prevents reading of the

user code with the On-Chip Debugger. Refer to the chapter Flash Option Bits on page 148

and the chapter On-Chip Debugger on page 167 for more information.

Flash Code Protection Against Accidental Program and Erasure

The Z8 Encore! XP® 4K Series provides several levels of protection against accidental

program and erasure of the Flash memory contents. This protection is provided by a com-

bination of the Flash Option bits, the register locking mechanism, the page select redun-

dancy and the sector level protection control of the Flash Controller.

Flash Code Protection Using the Flash Option Bits

The FRP and FWP Flash Option Bits combine to provide three levels of Flash Program

Memory protection as listed in Table 80. Refer to the chapter Flash Option Bits on

page 148 for more information.

FFREQ[15:0]

System Clock Frequency (Hz)

1000

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Caution:

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