mc56f801 Freescale Semiconductor, Inc, mc56f801 Datasheet - Page 82

• Manufacturer Part Number: mc56f801
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

7.1 Operation with Security Enabled
Once the user has programmed the Flash with his application code, the 56F8014 can be secured by
programming the security bytes located in the FM configuration field, which are located at the last 9 words
of Program Flash. These non-volatile bytes will keep the part secured through reset and through
power-down of the device. Only two bytes within this field are used to enable or disable security. Refer to
the Flash Memory chapter in the 56F801X Peripheral Reference Manual for the state of the security
bytes and the resulting state of security. When Flash security mode is enabled in accordance with the
method described in the Flash Memory module chapter, the 56F8014 will disable the core EOnCE debug
capabilities. Normal program execution is otherwise unaffected.
7.2 Flash Access Lock and Unlock Mechanisms
The 56F8014 has several operating functional and debug modes. Effective Flash security must address
operating mode selection and anticipate modes in which the on-chip Flash can be read without explicit user
permission.
7.2.1
On-chip Flash can be read by issuing commands across the EOnCE port, which is the debug interface for
the 56800E CPU. The TCLK, TMS, TDO, and TDI pins comprise a JTAG interface onto which the
EOnCE port functionality is mapped. When the 56F8014 boots, the chip-level JTAG TAP (Test Access
Port) is active and provides the chip’s boundary scan capability and access to the ID register, but proper
implementation of Flash security will block any attempt to access the internal Flash memory via the
EOnCE port when security is enabled.
7.2.2
If a user inadvertently enables security on the 56F8014, the only lockout recovery mechanism is the
complete erasure of the internal Flash contents, including the configuration field, and thus disables security
(the protection register is cleared). This does not compromise security, as the entire contents of the user’s
secured code stored in Flash are erased before security is disabled on the 56F8014 on the next reset or
power-up sequence.
To start the lockout recovery sequence, the JTAG public instruction (LOCKOUT_RECOVERY) must
first
LOCKOUT_RECOVERY instruction has been shifted into the instruction register, the clock divider value
must be shifted into the corresponding 7-bit data register. After the data register has been updated, the user
must transition the TAP controller into the RUN-TEST/IDLE state for the lockout sequence to commence.
The controller must remain in this state until the erase sequence has completed. Refer to the 56F801X
Peripheral Reference Manual for more details, or contact Freescale.
Note:
82
be
Disabling EOnCE Access
Flash Lockout Recovery Using JTAG
Once the lockout recovery sequence has completed, the user must reset both the JTAG TAP controller
(by advancing the TAP state machine to the reset state) and the 56F8014 (by asserting external chip
reset) to return to normal unsecured operation.
shifted
into
the
chip-level
56F8014 Technical Data, Rev. 9
TAP
controller’s
instruction
register.
Freescale Semiconductor
Once
Preliminary
the