Z8F021ASH020SC datasheet(183/276 Pages) ZILOG

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PS022815-0206

Non-Volatile Data Storage

Z8 Encore! XP® 4K Series

Product Specification

164

Byte Write

To write a byte to the NVDS array, the user code must first push the address, then the data

byte onto the stack. The user code issues a CALL instruction to the address of the byte-

write routine (0x10B3). At the return from the sub-routine, the write status byte resides in

working register R0. The bit fields of this status byte are defined in Table 106. The con-

tents of the status byte are undefined for write operations to illegal addresses. Also, user

code should pop the address and data bytes off the stack.

The write routine uses 13 bytes of stack space in addition to the two bytes of address and

data pushed by the user. Sufficient memory must be available for this stack usage.

Because of the flash memory architecture, NVDS writes exhibit a non-uniform execution

time. In general, a write takes 251

μs (assuming a 20MHz system clock). Every 400 to 500

writes, however, a maintenance operation is necessary. In this rare occurrence, the write

takes up to 61ms to complete. Slower system clock speeds result in proportionally higher

execution times.

NVDS byte writes to invalid addresses (those exceeding the NVDS array size) have no

effect. Illegal write operations have a 2

μs execution time.

Reserved—Must be 0.

RCPY—Recopy Subroutine Executed

A recopy subroutine was executed. These operations take significantly longer than a

normal write operation.

PF—Power Failure Indicator

A power failure or system reset occurred during the most recent attempted write to the

NVDS array.

AW—Address Write Error

An address byte failure occurred during the most recent attempted write to the NVDS

array.

DWE—Data Write Error

A data byte failure occurred during the most recent attempted write to the NVDS

array.

Table 106. Write Status Byte

BITS

FIELD

Reserved

RCPY

AWE

DWE

DEFAULT

VALUE

00000000

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