Freescale Semiconductor ColdFire MCF52210 - Manual (Page 330)

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MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
19-8 Freescale Semiconductor
19.6 Initialization/Application Information
Prior to issuing any program or erase commands, the clock configuration register must be written to set
the flash state machine clock (FCLK). The flash controller module runs at the system clock frequency
divide by 2, but FCLK must be divided down from this frequency to a frequency between 150 kHz and
200 kHz. Use the following procedure to set the PRDIV8 and DIV[5:0] bits in the clock configuration
register.
1. If f
SYS
is greater than 25.6 MHz, PRDIV8 = 1; otherwise PRDIV8 = 0.
2. Determine DIV[5:0] by using the following equation. Keep only the integer portion of the result
and discard any fraction. Do not round the result.
3. Therefore, the flash state machine clock is:
Therefore, for Fsys equaling 66 MHz, writing 0x54 to the clock configuration register sets Fclk to 196.43
kHz, which is a valid frequency for the timing of program and erase operations.
For proper program and erase operations, it is critical to set Fclk between 150 kHz and 200 kHz. Array
damage due to overstress can occur when Fclk is less than 150 kHz. Incomplete programming and erasure
can occur when Fclk is greater than 200 kHz.
DIV
Fsys
2x200kHzx 1 PRDIV8x7
( )
+
( )
------------------------------------------------------------------------------- =
Fclk
Fsys
2x DIV 1 +
( )x 1
PRDIV8x7
( )
+
( )
------------------------------------------------------------------------------------ =