Fast Ethernet Controller (FEC)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
45-24
Freescale Semiconductor
To generate an 802.3-compliant MII management interface write frame (write to a PHY register) the user
must write {01 01 PHYAD REGAD 10 DATA} to MII_DATA. Writing this pattern causes the control logic
to shift data out of MII_DATA following a preamble generated by the control state machine. When the
write management frame operation completes, the MII_DATAIO_COMPL interrupt is generated. At this
time the contents of MII_DATA 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 MII_DATA, (the content of the DATA field is a don’t care). Writing this
pattern causes the control logic to shift data out of MII_DATA following a preamble generated by the
control state machine. During this time, the contents of MII_DATA are serially shifted and are
unpredictable if read by the user. An MII_DATAIO_COMPL interrupt is generated when the read
management frame operation completes. At this time the contents of MII_DATA match the original value
written except for the DATA field, whose contents have been replaced by the value read from the PHY
register.
Writing to MII_DATA during frame generation alters the frame contents. Software should use the
MII_DATAIO_COMPL interrupt to avoid writing to the MII_DATA register during frame generation.
45.3.2.14 MII Speed Control Register (MII_SPEED)
The MII_SPEED register, shown in
Figure 45-18
, provides control of the MII clock (MDC pin) frequency
and allows the MII management frame preamble to be dropped. MII_SPEED is written by the user.
Table 45-21
describes MII_SPEED fields.
0
15
Field
—
Reset
0000_0000_0000_0000
R/W
R/W
Addr
0x0E84 (FEC1) & 0x1E84 (FEC2)
16
23
24
25
30
31
Field
—
DIS_PREAMBLE
MII_SPEED
—
Reset
0000_0000_0000_0000
R/W
R/W
Addr
0x0E86 (FEC1) & 0x1E86 (FEC2)
Figure 45-18. MII_SPEED Register
Table 45-21. MII_SPEED Field Descriptions
Bits
Name
Description
0–23
—
Reserved, should be cleared by the host processor.
24
DIS_PREAMBLE
Discard preamble. The MII standard allows the preamble to be dropped if the attached
PHY devices does not require it.
0 Preamble is not discarded.
1 Preamble (32 1s) is not prepended to the MII management frame.
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Страница 1162: ...Fast Ethernet Controller FEC MPC885 PowerQUICC Family Reference Manual Rev 2 45 40 Freescale Semiconductor ...
Страница 1172: ...SEC Lite Overview MPC885 PowerQUICC Family Reference Manual Rev 2 46 8 Freescale Semiconductor ...
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