Z8F0830HH020SG Datasheet, PDF (152/257 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore!^® F0830 Series
Product Specification
134
Nonvolatile Data Storage
Z8 Encore! F0830 Series devices contain a Nonvolatile Data Storage (NVDS) element of
up to 64 bytes (except when in Flash 12 KB mode). This type of memory can perform over
100,000 write cycles.
Operation
NVDS is implemented by special-purpose Zilog software stored in areas of program mem-
ory that are not user-accessible. These special-purpose routines use Flash memory to store
the data, and incorporate a dynamic addressing scheme to maximize the write/erase endur-
ance of the Flash.
Note: The products in the Z8 Encore! F0830 Series feature multiple NVDS array sizes. See the
Z8 Encore! F0830 Series Family Part Selection Guide section on page 2 for details.
NVDS Code Interface
Two routines are required to access the NVDS: a write routine and a read routine. Both of
these routines are accessed with a CALL instruction to a predefined address outside of pro-
gram memory that is accessible to the user. Both the NVDS address and data are single-
byte values. In order to not disturb the user code, these routines save the working register
set before using it so that 16 bytes of stack space are required to preserve the site. After
finishing the call to these routines, the working register set of the user code is recovered.
During both read and write accesses to the NVDS, interrupt service is not disabled. Any
interrupts that occur during NVDS execution must not disturb the working register and
existing stack contents; otherwise, the array can become corrupted. Zilog recommends the
user disable interrupts before executing NVDS operations.
Use of the NVDS requires 16 bytes of available stack space. The contents of the working
register set are saved before calling NVDS read or write routines.
For correct NVDS operation, the Flash Frequency registers must be programmed based on
the system clock frequency. See the Flash Operation Timing Using the Flash Frequency
Registers section on page 114.
PS025113-1212
Nonvolatile Data Storage