MC9S12NE64CPVE Datasheet, PDF (335/554 Pages) Freescale Semiconductor, Inc – MC9S12NE64 Device Overview

Functional Description
11.4.2.1 Address Recognition
The EMAC executes filtering by using the destination address of a receive frame and eliminates a frame
that does not satisfy a given condition. See Figure 11-24 for the address recognition algorithm.
11.4.2.1.1 Promiscuous Mode
If the PROM bit is set, promiscuous mode is enabled and all frames are accepted regardless of address.
The PROM bit does not affect any other filtering in the EMAC.
11.4.2.1.2 Unicast Filter
Unless the PROM bit is set, the 48-bit MAC address (MACAD) is compared for an exact match with the
destination address of a receive frame with an individual address (group bit is 0). If the unicast address of
the receive frame matches MACAD, the frame is accepted; otherwise, it is rejected.
11.4.2.1.3 Broadcast Filter
A broadcast frame (48-bit address of all 1s) is accepted if the BCREJ bit is 0 and rejected if the BCREJ bit
is 1 unless the PROM bit is set.
11.4.2.1.4 Multicast Filter
If the CONMC bit is set to 0, all multicast frames are accepted. If the CONMC bit is 1 and the PROM bit
is 0, only multicast frames with the hash table match are accepted.
The hash table algorithm operates as follows. The 48-bit destination address is mapped into one of 64 bits,
which are represented by the 64 bits stored in MCHASH. This mapping is performed by passing the 48-bit
address through the 32-bit CRC generator and selecting the 6 most significant bits of the CRC-encoded
result to generate a number between 0 and 63. If the CRC generator selects a bit that is set in the hash table,
the frame is accepted; otherwise, it is rejected. To set the hash table, the CRC of a multicast address must
be calculated and the corresponding bit must be set in advance.
11.4.2.1.5 PAUSE Destination Address
If the EMAC is in full-duplex mode and the RFCE bit is set, the receiver detects incoming PAUSE frames.
A PAUSE frame has a 48-bit destination multicast address of 01-80-C2-00-00-01 or unique DA. Upon
detection of a PAUSE frame, the frame is temporarily accepted for further type/length recognition.
MC9S12NE64 Data Sheet, Rev. 1.1
Freescale Semiconductor
335