PIC18F97J60 Datasheet, PDF (247/474 Pages) Microchip Technology – 64/80/100-Pin, High-Performance, 1 Mbit Flash Microcontrollers with Ethernet

PIC18F97J60 FAMILY
18.8 Receive Filters
To minimize microcontroller processing overhead, the
Ethernet module incorporates a range of different
receive filters which can automatically reject packets
which are not needed. Six different types of packet
filters are implemented:
• Unicast
• Multicast
• Broadcast
• Pattern Match
• Magic Packet™
• Hash Table
The individual filters are all configured by the ERXFCON
register (Register 18-21). More than one filter can be
active at any given time. Additionally, the filters can be
configured by the ANDOR bit to either logically AND or
logically OR the tests of several filters. In other words,
the filters may be set so that only packets accepted by
all active filters are accepted, or a packet accepted by
any one filter is accepted. The flowcharts in Figure 18-11
and Figure 18-12 show the effect that each of the filters
will have, depending on the setting of ANDOR.
The device can enter Promiscuous mode and receive
all packets by clearing the ERXFCON register. The
proper setting of the register will depend on the
application requirements.
18.8.1 UNICAST FILTER
The Unicast receive filter checks the destination
address of all incoming packets. If the destination
address exactly matches the contents of the MAADR
registers, the packet will meet the Unicast filter criteria.
18.8.2 MULTICAST FILTER
The Multicast receive filter checks the destination
address of all incoming packets. If the Least Significant
bit of the first byte of the destination address is set, the
packet will meet the Multicast filter criteria.
18.8.3 BROADCAST FILTER
The Broadcast receive filter checks the destination
address of all incoming packets. If the destination
address is FF-FF-FF-FF-FF-FF, the packet will meet
the Broadcast filter criteria.
18.8.4 HASH TABLE FILTER
The Hash Table receive filter performs a CRC over the
six destination address bytes in the packet. The CRC is
then used as a pointer into the bits of the EHT registers.
If the pointer points to a bit which is set, the packet
meets the Hash Table filter criteria. For example, if the
CRC is calculated to be 05h, bit 5 in the Hash Table will
be checked. If it is set, the Hash Table filter criteria will
be met. If every bit is clear in the Hash Table, the filter
criteria will never be met. Similarly, if every bit is set in
the Hash Table, the filter criteria will always be met.
© 2006 Microchip Technology Inc.
Advance Information
DS39762A-page 245