MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
14-39
The Ethernet controller receives serial data LSB first.
14.4.8
Ethernet Address Recognition
The FEC filters the received frames based on the type of destination address (DA) — individual (unicast),
group (multicast), or broadcast (all-ones group address). The difference between an individual address and
a group address is determined by the I/G bit in the destination address field. A flowchart for address
recognition on received frames is illustrated in the figures below.
Address recognition is accomplished through the use of the receive block and microcode running on the
microcontroller. The flowchart shown in
illustrates the address recognition decisions made
by the receive block, while
illustrates the decisions made by the microcontroller.
If the DA is a broadcast address and broadcast reject (RCR[BC_REJ]) is deasserted, then the frame will
be accepted unconditionally, as shown in
. Otherwise, if the DA is not a broadcast address,
then the microcontroller runs the address recognition subroutine, as shown in
.
If the DA is a group (multicast) address and flow control is disabled, then the microcontroller will perform
a group hash table lookup using the 64-entry hash table programmed in GAUR and GALR. If a hash match
occurs, the receiver accepts the frame.
If flow control is enabled, the microcontroller will do an exact address match check between the DA and
the designated PAUSE DA (01:80:C2:00:00:01). If the receive block determines that the received frame
is a valid PAUSE frame, then the frame will be rejected. Note the receiver will detect a PAUSE frame with
the DA field set to either the designated PAUSE DA or the unicast physical address.
If the DA is the individual (unicast) address, the microcontroller performs an individual exact match
comparison between the DA and 48-bit physical address that the user programs in the PALR and PAUR
registers. If an exact match occurs, the frame is accepted; otherwise, the microcontroller does an individual
hash table lookup using the 64-entry hash table programmed in registers, IAUR and IALR. In the case of
an individual hash match, the frame is accepted. Again, the receiver will accept or reject the frame based
on PAUSE frame detection, shown in
.
If neither a hash match (group or individual), nor an exact match (group or individual) occur, then if
promiscuous mode is enabled (RCR[PROM] = 1), then the frame will be accepted and the MISS bit in the
receive buffer descriptor is set; otherwise, the frame will be rejected.
Similarly, if the DA is a broadcast address, broadcast reject (RCR[BC_REJ]) is asserted, and promiscuous
mode is enabled, then the frame will be accepted and the MISS bit in the receive buffer descriptor is set;
otherwise, the frame will be rejected.
In general, when a frame is rejected, it is flushed from the FIFO.
Summary of Contents for MPC5553
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