Z8F640x/Z8F480x/Z8F320x/Z8F240x/Z8F160x
Z8 Encore!®
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Flash Operation Timing Using the Flash Frequency Registers
Before performing either a program or erase operation on the Flash memory, the user must
first configure the Flash Frequency High and Low Byte registers. The Flash Frequency
registers allow programming and erasure of the Flash with system clock frequencies rang-
ing from 32KHz (32768Hz) through 20MHz.
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:.
System Clock Frequency (Hz)
---------------------------------------------------------------------------
FFREQ[15:0] =
1000
Caution:
Flash programming and erasure are not supported for system clock fre-
quencies below 32KHz (32768Hz) or above 20MHz. The Flash Frequency
High and Low Byte registers must be loaded with the correct value to in-
sure proper operation of the Z8F640x family device.
Flash Code Protection Against External Access
The user code contained within the Z8F640x family device’s Flash memory can be pro-
tected against external access via the On-Chip Debugger. Programming the RPOption Bit
prevents reading of the user code through the On-Chip Debugger. Refer to the Option Bits
chapter and the On-Chip Debugger chapter for more information.
Flash Code Protection Against Accidental Program and Erasure
The Z8F640x family device provides several levels of protection against accidental pro-
gram and erasure of the Flash memory contents. This protection is provided by a combina-
tion of the Option bits and the locking mechanism of the Flash Controller.
PS017610-0404
Flash Memory
ZILOG [ ZILOG, INC. ]
