Z8F042AHJ020SG Datasheet, PDF (193/282 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F082A Series
Product Specification
176
Nonvolatile Data Storage
The Z8 Encore! XP F082A Series devices contain a nonvolatile data storage (NVDS) ele-
ment of up to 128 bytes. This memory can perform over 100,000 write cycles.
Operation
The NVDS is implemented by special purpose Zilog software stored in areas of program
memory, which are not user-accessible. These special-purpose routines use the Flash
memory to store the data. The routines incorporate a dynamic addressing scheme to maxi-
mize the write/erase endurance of the Flash.
Note:
Different members of the Z8 Encore! XP F082A Series feature multiple NVDS array
sizes; see the Part Selection Guide section on page 2 for details. Devices containing 8 KB
of Flash memory do not include the NVDS feature.
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 the
user-accessible program memory. Both the NVDS address and data are single-byte values.
Because these routines disturb the working register set, user code must ensure that any
required working register values are preserved by pushing them onto the stack or by
changing the working register pointer just prior to NVDS execution.
During both read and write accesses to the NVDS, interrupt service is NOT disabled. Any
interrupts that occur during the NVDS execution must take care not to disturb the working
register and existing stack contents or else the array may become corrupted. Disabling
interrupts before executing NVDS operations is recommended.
Use of the NVDS requires 15 bytes of available stack space. Also, the contents of the
working register set are overwritten.
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 149).
PS022827-1212
PRELIMINARY
Nonvolatile Data Storage