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I test my design according to your advice, and the result shows MAC2 works as the same as MAC. With my 2nd experiment, a net-analysis instrument （smartbits）substitutes for PC2 and detects the receive packets. As a result, the ARP request packets have a CRC error. every packet occupy 78 bytes. the anterior 42 bytes is correct but the rule of latter 36 bytes is unkown. The follow is the receive packet when a ping command sends at side of PC1. I don’t know why CRC error occur？“ FF FF FF FF FF FF B8 CA 3A 8A 83 5A 08 06 00 01 08 00 06 04 00 01 B8 CA 3A 8A 83 5A C0 A8 00 03 00 00 00 00 00 00 C0 A8 00 37 5F 45 64 50 05 23 82 82 CA A2 6E A0 0A 0A 0A 0A 00 00 00 00 C0 A8 00 03 B8 CA 3A 8A 83 5A 00 00 64 98 C8 4A”
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Further test result reveals the 4-byte CRC value is incorrect at sink while other field of packets is received accurately. The weird thing is that only 4-bits of CRC field occur error, moreover, the wrong 4-bits is always a “4” as the pciture shows. I can observe that the CRC value outputed by MAC1 is variable and normal when the CRC function of MAC IP is canceled. I‘m puzzled what caused the regular CRC error？
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