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External CAM filtering
336
NS9750 Hardware Reference
Figure 69: RMII PHY receive interface
After performing the necessary destination address lookup, the incoming frame can
be rejected by the CAM filtering hardware by asserting the
CAM_REJECT(GPIO[20]) input
high, as shown in Figure 70.
CAM_REJECT(GPIO[20]) must be asserted no later than one
di-bit nibble before the end of the frame (that is, when
CRS_DV is negated). Once the
signal is asserted, it must remain asserted until
16 REF_CLKs (for 100 Mbps) or 128
REF_CLKS
(for 10 Mbps) after the end of the frame, to guarantee that the RX_WR logic
has captured it. For example, a 64-byte frame contains 256 di-bits (that is, 2 bits) of
data on the RMII interface.
CAM_REJECT must be valid by the 254
th
di-bit of data (the
first di-bit is 0
th
di-bit).
Figure 70: External Ethernet CAM filtering for RMII PHY
00 01 01 01
01
11
10
00
11 11
Preamble
REF_CLK
RXD[1:0]
00
00
01 01 01
10
11
CRS_DV
SFD
Packet Data
Note 1
1. Rising edge of CRS_DV asynchronous relative to REF_CLK
2. CRS_DV synchronous to REF_CLK once RXD[1:0] changes from "00"
to "01" at start of preamble.
11 00 00 00
00
00
00
00
00 00
REF_CLK
RXD[1:0] 01
10
00 00 00
00
00
CRS_DV Note 1
1. Falling edge of CRS_DV synchronous relative to REF_CLK.
CAM_REJECT
REJECT setup to end of Packet
(1 REF_CLK min)
REJECT hold from end of packet
(16/128 REF_CLKs min for 100/10Mbps)