MCF548x Reference Manual, Rev. 3
30-48 Freescale Semiconductor
During reception, the Ethernet controller checks for various error conditions and once the entire frame is
written into the FIFO, a 32-bit frame status word (RFSW) is written into the FIFO. This receive frame
status word contains the M, BC, MC, LG, NO, CR, OF and TR status bits, and the frame length. See
Section 30.4.12.2, “Reception Errors” for more details.
Receive frames are not truncated if they exceed the max frame length (MAX_FL); however, the BABR
interrupt will occur and the LG bit in the receive frame status word (RFSW) will be set. See
Section 30.4.2.1, “Receive Frame Status Word (RFSW)” for more details.
The FEC receives serial data LSB first.

30.4.6 Ethernet Address Recognition

The FEC filters the received frames based on destination address (DA) type — 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.
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 Figure 30-41. Otherwise, if the DA is not a broadcast address,
then the microcontroller runs the address recognition subroutine.
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. See Section 30.4.8,
“Full Duplex Flow Control,” for more details on pause frames.
If the DA is the individual (unicast) address, the microcontroller performs an individual exact match
comparison between the DA and the 48-bit physical address that the user programs in the PALR and PAHR
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 Figure 30-41.
If neither a hash match (group or individual) nor an exact match (group or individual) occur, and if
promiscuous mode is enabled (RCR[PROM] = 1), then the frame will be accepted and the MISS bit in the
RFSW will be cleared; 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.
The flowchart shown in Figure 30-41 illustrates the address recognition decisions made by the receive
block.