ENC424J600 datasheet(97/168 Pages) MICROCHIP

97 / 168 page

 2010 Microchip Technology Inc.

DS39935C-page 95

ENC424J600/624J600

10.0 RECEIVE FILTERS

To minimize the number of frames that the host controller

must process, ENC424J600/624J600 devices incorpo-

rate 11 different receive filters to discard unwanted

frames. The following filters are available:

• CRC Error Collection Filter

• Runt Error Collection Filter

• CRC Error Rejection Filter

• Runt Error Rejection Filter

• Unicast Collection Filter

• Not-Me Unicast Collection Filter

• Multicast Collection Filter

• Broadcast Collection Filter

• Hash Table Collection Filter

• Magic Packet™ Collection Filter

• Pattern Match Collection Filter

Each filter is software configurable, and can be individu-

ally enabled or disabled, using the ERXFCON register

(Register 10-1). Each filter is either a Collection or a

Rejection filter, with incoming frames passing sequen-

tially through each enabled filter. The first filter to make a

definitive decision for a frame takes priority over all

others. Collection filters either force a frame to be

accepted or defer the decision to a lower priority filter.

Similarly, Rejection filters either discard frames or defer

to lower priority filters. Frames that pass through all filters

without specifically being accepted are discarded.

Figure 10-1 demonstrates this decision tree.

At power-up, the CRC Error Rejection, Runt Error

Rejection, Unicast Collection and Broadcast Collection

filters are enabled, and all others are disabled. With

these settings, the device will only accept Broadcast

frames and frames specifically addressed to the local

MAC address. Invalid frames and those destined for

other nodes will be automatically rejected.

Note 1:

The MAC internally processes and filters

Ethernet control frames as they arrive

and before they reach these filters. For

the application to receive Ethernet control

frames, enable the PASSALL option

(MACCON1<1> = 1).

If the Ethernet Receive Enable bit, RXEN

(ECON1<0>), is set, the filters may make

an incorrect decision if any of the receive

filters are reconfigured at the exact

moment a new frame is being received.

To avoid this behavior, clear the RXEN bit

prior to changing any receive filter

settings.

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