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Direct ETH MAC MII to MAC MII connection

Question asked by Alan Knight on Jun 2, 2020
Latest reply on Jun 10, 2020 by Alan Knight

I have a ASIC chip which has a Ethernet MAC MII interface (10/100 speed) and it needs to talk to a CPU (NXP i.MX6 processor family) which also has a MAC MII interface & USB2 interface. I've read that you can't connect MAC MII to MAC MII directly without a PHY - the protocol won't work. Is that true? Basically I need an expert on Ethernet IEEE 802.3.

I have read on some forums where MAC-MAC connections (RMII, RGMII, SGMII) without PHY may have worked though.

Direct MAC-MAC connection to Ethernet switch without a PHY 

i.MX6 GMAC to GMAC connection 

mac to mac connection,bandwidth 10Mbits/sec 

Direct MAC to MAC connection 

 

Otherwise I have read this on direct MAC-MAC physical connections. But I don't know if this has ever been tried.

http://caxapa.ru/thumbs/414271/Schematic_Design_Guideline%2C_MAC-to-MAC_M.pdf 

 

Otherwise I need some sort of 'bridge' chip to connect the two together. 
I think there are two possible solutions:-
1) Use a 2-port ETH Switch chip and connect the PHY's together. Therefore ASIC MAC MII to ETH SW MAC MII, short both PHY outputs together, then ETH SW MAC MII to CPU MAC MII. Possibly NXP TJA1102.
2) Use a USB2 to PHY bridge. Though I can't find one that outputs a MAC MII interface. I presume I have to connect it to another single port ETH PHY/MII chip (i.e. similar to option 1 above).


Notes:

1) ASIC VIO is 1.8V

2) The EMAC IP core used in the ASIC is Overview :: 10_100_1000 Mbps tri-mode ethernet MAC :: OpenCores  , this does NOT produce a 25MHz ref CLK. Therefore an external one is required.

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