Functional Overview
Table 3−4. Boot Mode Selection
GPIOF4
GPIOF12
GPIOF3
(SPISTEA)
No PU
x
GPIOF2
(SPICLK)
No PU
x
(SCITXDA)
(MDXA)
No PU
x
†
Mode Selected
PU
1
Jump to Flash/ROM address 0x3F 7FF6
A branch instruction must have been programmed here prior to
reset to re−direct code excution as desired.
Call SPI_Boot to load from an external serial SPI EEPROM
Call SCI_Boot to load from SCI-A
0
0
0
0
0
1
0
0
0
0
x
1
1
0
0
x
1
0
1
0
Jump to H0 SARAM address 0x3F 8000
Jump to OTP address 0x3D 7800
Call Parallel_Boot to load from GPIO Port B
†
‡
§
PU = pin has an internal pullup No PU = pin does not have an internal pullup
Extra care must be taken due to any affect toggling SPICLK to select a boot mode may have on external logic.
If the boot mode selected is Flash, H0, or OTP, then no external code is loaded by the bootloader.
3.2.11 Security
The F281x and C281x support high levels of security to protect the user firmware from being
reverse-engineered. The security features a 128-bit password (hardcoded for 16 wait states), which the user
programs into the flash. One code security module (CSM) is used to protect the flash/ROM/OTP and the L0/L1
SARAM blocks. The security feature prevents unauthorized users from examining the memory contents via
the JTAG port, executing code from external memory or trying to boot-load some undesirable software that
would export the secure memory contents. To enable access to the secure blocks, the user must write the
correct 128-bit ”KEY” value, which matches the value stored in the password locations within the Flash/ROM.
NOTE:
For code security operation, all addresses between 0x3F7F80 and 0x3F7FF5 cannot be used
as program code or data, but must be programmed to 0x0000 when the Code Security
Passwords are programmed. If security is not a concern, then these addresses may be used
for code or data.
The 128-bit password (at 0x3F 7FF8 − 0x3F 7FFF) must not be programmed to zeros. Doing
so would permanently lock the device.
Code Security Module Disclaimer
The Code Security Module (“CSM”) included on this device was designed to password
protect the data stored in the associated memory (either ROM or Flash) and is warranted
by Texas Instruments (TI), in accordance with its standard terms and conditions, to
conform to TI’s published specifications for the warranty period applicable for this device.
TI DOES NOT, HOWEVER, WARRANT OR REPRESENT THAT THE CSM CANNOT BE
COMPROMISED OR BREACHED OR THAT THE DATA STORED IN THE
ASSOCIATED MEMORY CANNOT BE ACCESSED THROUGH OTHER MEANS.
MOREOVER, EXCEPT AS SET FORTH ABOVE, TI MAKES NO WARRANTIES OR
REPRESENTATIONS CONCERNING THE CSM OR OPERATION OF THIS DEVICE,
INCLUDING ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR
A PARTICULAR PURPOSE.
37
April 2001 − Revised December 2004
SPRS174L
TI [ TEXAS INSTRUMENTS ]
