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Ethernet Module
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
11-18
Freescale Semiconductor
To generate an MII management interface read frame (read a PHY register), the user must write {01 10
PHYAD REGAD 10 XXXX} to MMFR (the contents of the DATA field are a don’t care). Writing this
pattern causes the control logic to shift out the data in the MMFR register following a preamble generated
by the control state machine.The contents of the MMFR register are altered as the contents are serially
shifted, and are unpredictable if read by the user. Once the read management frame operation completes,
the MII interrupt is generated. At this time the contents of the MMFR register matches the original value
written except for the DATA field, whose contents are replaced by the value read from the PHY register.
If the MMFR register is written while frame generation is in progress, the frame contents are altered.
Software should use the MII interrupt to avoid writing to the MMFR register while frame generation is in
progress.
11.5.8
MII Speed Control Register (MSCR)
The MSCR register,
, provides control of the MII clock (E_MDC pin) frequency, allows
dropping the preamble on the MII management frame and provides observability (intended for
manufacturing test) of an internal counter used in generating the E_MDC clock signal.
31
16
Field
—
Reset
0000_0000_0000_0000
R/W
Read/Write
15
8
7
6
1
0
Field
—
DIS_PREAMBLE
MII_SPEED
—
Reset
0000_0000
0
000_000
0
R/W
Read/Write
Addr
MBAR + 0x884
Figure 11-12. MII Speed Control Register (MSCR)
Table 11-14. MSCR Field Descriptions
Bits
Name
Description
31–8
—
Reserved, should be cleared.
7
DIS_PREAMBLE
Disable preamble. Asserting this bit causes the preamble of 32 consecutive 1’s not to be
prepended to the MII management frame. The MII standard allows the preamble to be dropped
if the attached PHY device(s) do not require it.
6–1
MII_SPEED
MII frequency divider. MII_SPEED controls the frequency of the MII management interface
clock (E_MDC) relative to system clock. A value of 0 in this field turns off the E_MDC and
leaves it in low-voltage state. Any non-zero value results in an E_MDC frequency given by the
following formula:
MDC_FREQUENCY = system frequency / (4 * MII_SPEED)
0
—
Reserved, should be cleared.
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