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:
.
System Clock Frequency (Hz)
FFREQ[15:0] = ---------------------------------------------------------------------------
1000
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.
Caution:
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 FRPFlash 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 FRPand FWPFlash 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.
PS022815-0206
Flash Memory
ZILOG [ ZILOG, INC. ]
