MC56F836 Freescale Semiconductor, Inc, MC56F836 Datasheet - Page 131

• Manufacturer Part Number: MC56F836
• Description: 56f8300 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

Flash Access Blocking Mechanisms
Proper implementation of Flash security requires that no access to the EOnCE port is provided when
security is enabled. The 56800E core has an input which disables reading of internal memory via the
JTAG/EOnCE. The FM sets this input at reset to a value determined by the contents of the FM security
bytes.
7.2.3
Flash Lockout Recovery
If a user inadvertently enables Flash security on the device, a built-in lockout recovery mechanism can be
used to reenable access to the device. This mechanism completely reases all on-chip Flash, thus disabling
Flash security. Access to this recovery mechanism is built into CodeWarrior via an instruction in memory
configuration (.cfg) files. Add, or uncomment the following configuration command:
unlock_flash_on_connect 1
For more information, please see CodeWarrior MC56F83xx/DSP5685x Family Targeting Manual.
The LOCKOUT_RECOVERY instruction has an associated 7-bit Data Register (DR) that is used to
control the clock divider circuit within the FM module. This divider, FM_CLKDIV[6:0], is used to control
the period of the clock used for timed events in the FM erase algorithm. This register must be set with
appropriate values before the lockout sequence can begin. Refer to the JTAG section of the 56F8300
Peripheral User Manual for more details on setting this register value.
The value of the JTAG FM_CLKDIV[6:0] will replace the value of the FM register FMCLKD that divides
down the system clock for timed events, as illustrated in
Figure
7-1. FM_CLKDIV[6] will map to the
PRDIV8 bit, and FM_CLKDIV[5:0] will map to the DIV[5:0] bits. The combination of PRDIV8 and DIV
must divide the FM input clock down to a frequency of 150kHz-200kHz. The “Writing the FMCLKD
Register” section in the Flash Memory chapter of the 56F8300 Peripheral User Manual gives specific
equations for calculating the correct values.
Flash Memory
SYS_CLK
input
DIVIDER
clock
2
7
FMCLKD
7
7
FM_CLKDIV
JTAG
FM_ERASE
Figure 7-1 JTAG to FM Connection for Lockout Recovery
56F8365 Technical Data, Rev. 7
Freescale Semiconductor
131
Preliminary