W5500 Hardware BUG for ARP request& macraw

Question

I have OMRON PLC act as TCP client, and a custom w5500 based board as TCP server. Basically, the w5500 ignores all arp request from OMRON, although it accepts arp request from PC. while trying to solve the issue, I opened a raw mac socket on w5500, listening and responding to ARP requests. BUT THE RESULT IS THE SAME! the w5500 chip filtered out all the ARP reply I sent to OMRON, but everything I sent to PC is ok. I tried the chip on another Semiens PLC, the same result. Now I really have no idea how to solve this issue then replacing w5500 with a difference phy chip.

mistree · Answer

After more testing, it’s clearly the w5500 has an internal blacklist for servral PLC brand mac address. This chip really sucks. I tested it with modifying arp reply dst mac. even if I change 1 byte, the reply got sent. The second byte of mac address is used for vendor identification, and w5500 blacklist some vendor(only if second byte is 0) for unknown purpose, this readlly sucks, and it’s not mentioned any where.