EXAMPLE 1: If the system clock is the 8MHz crystal frequency because the PLL has not been set up,
the input clock will be below 12.8MHz, so PRDIV8 = FM_CLKDIV[6] = 0. Using the following equation
yields a DIV value of 19 for a clock of 200kHz, and a DIV value of 20 for a clock of 190kHz. This
translates into an FM_CLKDIV[6:0] value of $13 or $14, respectively.
SYS_CLK
( )
(2)
150[kHz]
200[kHz]
<
<
(DIV + 1)
EXAMPLE 2: In this example, the system clock has been set up with a value of 32MHz, making the FM
input clock 16MHz. Because that is greater than 12.8MHz, PRDIV8 = FM_CLKDIV[6] = 1. Using the
following equation yields a DIV value of 9 for a clock of 200kHz, and a DIV value of 10 for a clock of
181kHz. This translates to an FM_CLKDIV[6:0] value of $49 or $4A, respectively.
SYS_CLK
( )
(2)
150[kHz]
200[kHz]
<
<
(DIV + 1)
Once the 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.
For details, see the JTAG Section in the 56F8300 Peripheral User Manual.
Note:
When the lockout recovery sequence has completed, the user must reset both the JTAG TAP controller
(by asserting TRST) and the device (by asserting external chip reset) to return to normal unsecured
operation.
7.2.4
Product Analysis
The recommended method of unsecuring a programmed device for product analysis of field failures is via
56F8345 Technical Data, Rev. 17
124
Freescale Semiconductor
Preliminary
FREESCALE [ Freescale ]
