10- Lock Bits, Fuse Bits and
Boot Loader
Boot Loader Support – Read-While-Write SelfProgramming:
• The Boot Loader Support provides a real Read-While-Write
Self-Programming mechanism for downloading and
uploading program code by the MCU itself. This feature
allows flexible application software updates controlled by
the MCU using a Flash-resident Boot Loader program.
• The program code within the Boot Loader section has the
capability to write into the entire Flash, including the Boot
Loader memory. The Boot Loader can thus even modify
itself, and it can also erase itself from the code if the
feature is not needed anymore. The size of the Boot Loader
memory is configurable with Fuses
Memory Programming:
1. Lock Bits:
Programming and Verification of EEPROM and Flash:
Lock
Bits
Protection Type
LB2
LB1
1
1
No memory lock features enabled
1
0
Further programming of the Flash and EEPROM
is disabled. The Fuse bits are locked in both
Serial and Parallel Programming mode
0
0
Further programming and Verification of the
Flash and EEPROM is disabled. The Fuse bits are
locked in both Serial and Parallel Programming
mode
Restrictions for SPM or LPM accessing the Application section:
Lock
Bits
Protection Type
BLB02
BLB01
1
1
No restrictions for SPM or LPM accessing the
Application section
1
0
SPM is not allowed to write to the Application
section
0
0
SPM is not allowed to write to the Application
section, and LPM executing from the Boot Loader
section is not allowed to read from the Application
section
0
1
LPM executing from the Boot Loader section is not
allowed to read from the Application section
Restrictions for SPM or LPM accessing the Boot Loader:
Lock
Bits
Protection Type
BLB12
BLB11
1
1
No restrictions for SPM or LPM accessing the
Boot Loader
1
0
SPM is not allowed to write to the Boot Loader
0
0
SPM is not allowed to write to the Boot Loader
section, and LPM executing from the Application
section is not allowed to read from the Boot
Loader
0
1
LPM executing from the Application section is
not allowed to read from the Boot Loader
section
2. Fuse Bits:
The ATmega16 has two fuse bytes. Note that the fuses are read
as logical zero, “0”, if they are programmed.
Notes:
•JTAG (Joint Test Action Group)boundary scan started as a
method of testing ICs and their interconnections using a shift
register built into the chip so that inputs could be shifted in
and the resulting outputs could be shifted out using only four
I/O pins (clock, input data, output data, and state machine
mode control). This eliminated the need for complex and
expensive, bed-of-nails cards for low-speed probing of IC I/O
pins.
When used as a debugging tool, an in circuit emulator- which
in turn uses JTAG as the transport mechanism - enables a
programmer to access an on-chip debug module which is
integrated into the CPU, via the JTAG interface. The debug
module enables the programmer to debug the software of an
embedded system.
OCDEN: On-Chip Debug System Enable
•
•
Signature Bytes :
All Atmel microcontrollers have a three-byte signature code
which identifies the device. This code can be read in both
serial and parallel mode, also when the device is locked.
The three bytes reside in a separate address space.
For the ATmega16 the signature bytes are:
1. $000: $1E (indicates manufactured by Atmel)
2. $001: $94 (indicates 16KB Flash memory)
3. $002: $03 (indicates ATmega16 device when $001 is $94)