Z8 Encore! XP® F08xA Series
Product Specification
130
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 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
Flash programming and erasure are not supported for system clock frequencies below
32KHz (32768Hz) or above 20MHz. The Flash Frequency High and Low Byte registers
must be loaded with the correct value to ensure operation of the Z8 Encore! XP® F08xA
Series devices.
Caution:
Flash Code Protection Against External Access
The user code contained within the Flash memory can be protected against external access
with the On-Chip Debugger. Programming the FRPFlash Option Bit prevents reading of
the user code with the On-Chip Debugger. Refer to the chapter “Flash Option Bits” on page 138
and the chapter “On-Chip Debugger” on page 148 for more information.
Flash Code Protection Against Accidental Program and Erasure
The Z8 Encore! XP® F08xA 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 FHSWPand FWPFlash Option Bits combine to provide three levels of Flash Program
Memory protection as listed in Table 78. Refer to the chapter “Flash Option Bits” on page 138
for more information.
PS024705-0405
P R E L I M I N A R Y
Flash Memory
ZILOG [ ZILOG, INC. ]
