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MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
14-18
Freescale Semiconductor
To perform a read or write operation on the MII management interface, the MMFR register must be written
by the user. To generate a valid read or write management frame, the ST field must be written with a 01
pattern, and the TA field must be written with a 10. If other patterns are written to these fields, a frame will
be generated but will not comply with the IEEE
802.3 MII definition.
To generate an IEEE
802.3-compliant MII management interface write frame (write to a PHY register),
the user must write {01 01 PHYAD REGAD 10 DATA} to the MMFR register. Writing this pattern will
cause the control logic to shift out the data in the MMFR register following a preamble generated by the
control state machine. During this time the contents of the MMFR register will be altered as the contents
are serially shifted and will be unpredictable if read by the user. After the write management frame
operation has completed, the MII interrupt will be generated. At this time the contents of the MMFR
register will match the original value written.
To generate an MII management interface read frame (read a PHY register) the user must write {01 10
PHYAD REGAD 10 XXXX} to the MMFR register (the content of the DATA field is a don’t care). Writing
this pattern will cause the control logic to shift out the data in the MMFR register following a preamble
generated by the control state machine. During this time the contents of the MMFR register will be altered
as the contents are serially shifted, and will be unpredictable if read by the user. After the read management
frame operation has completed, the MII interrupt will be generated. At this time the contents of the MMFR
register will match the original value written except for the DATA field whose contents have been replaced
by the value read from the PHY register.
If the MMFR register is written while frame generation is in progress, the frame contents will be altered.
Software should software should poll the EIR[MII] bit or use the EIR[MII] bit to generate an interrupt to
avoid writing to the MMFR register while frame generation is in progress.
14.3.4.2.7
MII Speed Control Register (MSCR)
The MSCR provides control of the MII clock (FEC_MDC signal) frequency, allows a preamble drop on
the MII management frame, and provides observability (intended for manufacturing test) of an internal
counter used in generating the FEC_MDC clock signal.
Table 14-10. MMFR Field Descriptions
Bit
Name
Description
0–1
ST
Start of frame delimiter. These bits must be programmed to 01 for a valid MII
management frame.
2–3
OP
Operation code. This field must be programmed to 10 (read) or 01 (write) to
generate a valid MII management frame. A value of 11 will produce “read”
frame operation while a value of 00 will produce “write” frame operation, but
these frames will not be MII compliant.
4–8
PA
PHY address. This field specifies one of up to 32 attached PHY devices.
9–13
RA
Register address. This field specifies one of up to 32 registers within the
specified PHY device.
14–15
TA
Turn around. This field must be programmed to 10 to generate a valid MII
management frame.
16–31
DATA
Management frame data. This is the field for data to be written to or read from
the PHY register.
Содержание MPC5553
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