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To All,

I am refering to LM3S9B96 device.

The following sections are copied from two different version of the LM3S9B96 data sheet.

From manual: Stellaris® LM3S9B96 Microcontroller DATA SHEET January 14, 2011

6.2.3.6 Nonvolatile Register Programming
This section discusses how to update registers that are resident within the Flash memory itself.
These registers exist in a separate space from the main Flash memory array and are not affected
by an ERASE or MASS ERASE operation. The bits in these registers can be changed from 1 to 0
with a write operation. The register contents are unaffected by any reset condition except power-on
reset, which returns the register contents to 0xFFFF.FFFF. By committing the register values using
the COMT bit in the FMC register, the register contents become nonvolatile and are therefore retained
following power cycling. Once the register contents are committed, the only way to restore the factory
default values is to perform the sequence described in “Recovering a "Locked"
Microcontroller” on page 192.

From manual: Stellaris® LM3S9B96 Microcontroller DATA SHEET January 20, 2012
6.2.3.6 Non-Volatile Register Programming
This section discusses how to update the registers shown in Table 6-2 on page 315 that are resident
within the Flash memory itself. These registers exist in a separate space from the main Flash memory
array and are not affected by an ERASE or MASS ERASE operation. With the exception of the Boot
Configuration (BOOTCFG) register, the settings in these registers can be written, their functions
verified, and their values read back before they are committed, at which point they become
non-volatile. If a value in one of these registers has not been committed, any type of reset restores
the last committed value or the default value if the register has never been committed. Once the
register contents are committed, the only way to restore the factory default values is to perform the
sequence described in “Recovering a "Locked" Microcontroller” on page 193.
To write to a non-volatile register:
■ Bits can only be changed from 1 to 0.

Page  335
Register 15: User Register 0 (USER_REG0), offset 0x1E0
Note: Offset is relative to System Control base address of 0x400FE000.
This register provides 31 bits of user-defined data that is non-volatile and can only be committed
once. Bit 31 indicates that the register is available to be committed and is controlled through hardware
to ensure that the register is only committed once. Prior to being committed, bits can only be changed
from 1 to 0. The reset value shown only applies to power-on reset; any other type of reset does not
affect this register. The write-once characteristics of this register are useful for keeping static
information like communication addresses that need to be unique per part and would otherwise
require an external EEPROM or other non-volatile device. Once committed, the only way to restore
the factory default value of this register is to perform the sequence detailed in “Recovering a "Locked"
Microcontroller” on page 193.

User Register 0 (USER_REG0)
Base 0x400F.E000
Offset 0x1E0
Type R/W, reset 0xFFFF.FFFF

Register 16: User Register 1 (USER_REG1), offset 0x1E4
Note: Offset is relative to System Control base address of 0x400FE000.
This register provides 31 bits of user-defined data that is non-volatile and can only be written once.
Bit 31 indicates that the register is available to be written and is controlled through hardware to
ensure that the register is only written once. The write-once characteristics of this register are useful
for keeping static information like communication addresses that need to be unique per part and
would otherwise require an external EEPROM or other non-volatile device.

User Register 1 (USER_REG1)
Base 0x400F.E000
Offset 0x1E4
Type R/W, reset 0xFFFF.FFFF

The documentation on USER_REG0 indicates that The reset value shown only applies to power-on reset; any other type of reset does not
affect this register.

The USER_REG1 does not have the note that reset values applies only to power on reset.

My testing shows that on push button reset, power on reset and soft reset the register are set to value of 0xFFFF.FFFF.

Q.1 Is there a typo in the manual on what reset the USER_REG0 and USER_REG1 are set to value of  0xFFFF.FFFF?

My testing indicates that  USER_REG0 and USER_REG1 value can be set to any value affter their content is 0xFFFF.FFFF. But once the content is set the follwoing comment seems to be valid "Prior to being committed, bits can only be changed from 1 to 0."

Q,2 can you confirm this?

Thanks.

With Best Regards,

Al Modi

Q.2