Z8F1680SH020SG Datasheet, PDF (315/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
290
Chapter 22. Nonvolatile Data Storage
The Z8 Encore! XP F1680 Series devices contain a Nonvolatile Data Storage (NVDS) ele-
ment of up to 256 bytes. This memory can perform over 100,000 write cycles.
22.1. Operation
The NVDS is implemented by special purpose Zilog^® software stored in areas of Program
Memory not accessible to you. These special-purpose routines use Flash memory to store
the data. The routines incorporate a dynamic addressing scheme to maximize the Write/
Erase endurance of the Flash.
Note: Different members of the Z8 Encore! XP F1680 Series feature multiple NVDS array sizes.
For more details, see Table 1 on page 2.
22.2. 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 the
program memory accessible to you. Both the NVDS address and data are single-byte val-
ues. In order NOT to disturb the user code, these routines save the working register set
before using it, so 16 bytes of stack space is needed 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 the NVDS execution must not disturb the working register and
existing stack contents; or else the array becomes corrupted. Disabling interrupts before
executing NVDS operations is recommended.
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. For more details, see the Flash Operation Timing Using Flash
Frequency Registers section on page 267.
PS025015-1212
PRELIMINARY
Nonvolatile Data Storage