![Freescale Semiconductor MCF52230 ColdFire Скачать руководство пользователя страница 376](http://html1.mh-extra.com/html/freescale-semiconductor/mcf52230-coldfire/mcf52230-coldfire_reference-manual_2330648376.webp)
EzPort
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
21-8
21.6
Initialization/Application Information
Prior to issuing any program or erase commands, the CFMCLKD register (see
“CFMCLKD — CFM Clock Divider Register,” on page 17-8
) must be written to set the flash state
machine clock (FCLK). The flash controller module runs at the system clock frequency divided 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/2
is greater than 25.6 MHz, PRDIV8 equals 1; otherwise, PRDIV8 equals 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.
The flash state machine clock is:
For Fsys equaling 60 MHz, DIV equals 18 (0b00010010) using the above equations, and writing 0x52
(0b01010010, i.e. including the PRDIV8 bit) to CFMCLKD sets FCLK to 197.37 kHz. This 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
2
200
×
kHz
1
PRDIV8
7
×
(
)
+
(
)
×
--------------------------------------------------------------------------------------
=
FCLK
Fsys
2
DIV
1
+
(
)
×
1
PRDIV8
7
×
(
)
+
(
)
×
--------------------------------------------------------------------------------------------
=
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60