10.0 Functional Description (Continued)
20006361
FIGURE 6. RAM Organization
= 0
Security disabled. Flash Memory read and write
are allowed.
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.
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. G1 pin is
WATCHDOG output with weak pullup.
Bit 1
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.
= 1
= 0
HALT mode disabled.
HALT mode enabled.
Bit 0
= 1
Execution following RESET will be from Flash
Memory.
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.
= 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 format of the Option register is as follows:
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
The following examples illustrate the declaration of the Op-
tion Register.
WATCH
DOG
Reserved
SECURITY
Reserved
HALT
FLEX
Syntax:
Bits 7, 6 These bits are reserved and must be 0.
Bit 5
[label:].sect
.db
config, conf
value ;1 byte,
;configures
= 1
Security enabled. Flash Memory read and write
are not allowed except in User ISP/Virtual E2 com-
mands. Mass Erase is allowed.
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