COP8-REF-AM datasheet(18/83 Pages) NSC

18 / 83 page

10.0 Functional Description (Continued)

10.4.1 Virtual EEPROM

The Flash memory and the User ISP functions (see Section

5.7), provide the user with the capability to use the flash

program memory to back up user defined sections of RAM.

This effectively provides the user with the same nonvolatile

data storage as EEPROM. Management, and even the

amount of memory used, are the responsibility of the user,

however the flash memory read and write functions have

been provided in the boot ROM.

One typical method of using the Virtual EEPROM feature

would be for the user to copy the data to RAM during system

initialization, periodically, and if necessary, erase the page of

Flash and copy the contents of the RAM back to the Flash.

10.5 OPTION REGISTER

The Option register, located at address 0x1FFF in the Flash

Program Memory, is used to configure the user selectable

security, WATCHDOG, and HALT options. The register can

be programmed only in external Flash Memory programming

or ISP Programming modes. Therefore, the register must be

programmed at the same time as the program memory. The

contents of the Option register shipped from the factory read

00 Hex.

The format of the Option register is as follows:

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Reserved

SECURITY

Reserved

WATCH

DOG

HALT

FLEX

Bits 7, 6 These bits are reserved and must be 0.

Bit 5

= 1

Security enabled. Flash Memory read and write

are not allowed except in User ISP/Virtual E

2 com-

mands. Mass Erase is allowed.

= 0

Security disabled. Flash Memory read and write

are allowed.

Bits 4, 3 These bits are reserved and must be 0.

Bit 2

= 1

WATCHDOG feature disabled. G1 is a general

purpose I/O.

= 0

WATCHDOG

feature

enabled.

WATCHDOG output with weak pullup.

Bit 1

= 1

HALT mode disabled.

= 0

HALT mode enabled.

Bit 0

= 1

Execution following RESET will be from Flash

Memory.

= 0

Flash Memory is erased. Execution following RE-

SET will be from Boot ROM with the MICROWIRE/

PLUS ISP routines.

The COP8 assembler defines a special ROM section type,

CONF, into which the Option Register data may be coded.

The Option Register is programmed automatically by pro-

grammers that are certified by National.

The user needs to ensure that the FLEX bit will be set when

the device is programmed.

The following examples illustrate the declaration of the Op-

tion Register.

Syntax:

[label:].sect

config, conf

.db

value

;1 byte,

;configures

20006361

FIGURE 6. RAM Organization

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