Ethernet doubts

[Bjtpower_magic]

Hi,
Its very late to ask after i worked on Ethernet but i havent understoon ethernet very well.
I have questions related to MII and RMII ethernet speeds.

I have seen both are supports to 10MBPS/100MBPS and how does it relates with Clock of Phy? What is relation?
In MII, We have 25MHZ clock and supports 100 MHZ While RMII- We have 50 MHZ Clock and supports 10/100MBPS.

What is corelation with speed vs frquency?

 

[KlausST]

Hi,

I guess you are talking about an IC with two interfaces:
* ethernet on the one side
* MII / RMII on the other side.

Timing, data transfer, protocol are completeley different for both interfaces. They don´t need to "correlate".

***
Similar to ENC28J60 which has
* ethernet on one side
* and SPI on the other side.

***
Other ICs with two interfaces:
* SPI to UART
* parallel to UART
* parallel to Profibus(R)
* USB to UART
... and so on

Klaus

 

[FvM]

MII protocol switches clock frequency between 10 and 100 MBPS operation, RMII uses constant 50 MHz and toggles enable signal. Check datasheets of PHY chips with MII and RMII interface, e.g. SMSC/Microchip 8700.

 

[Bjtpower_magic]

Thank you for replies and i had done some study for SMSC Application notes.
Please clarify few doubts.
What is SMC (MDC and MDIO)?
Why we need TX (3:0) and RX (3:0) when we have MDIO?

Please help me with significance of both?

 

[KlausST]

Hi,

Why riddles?
Why no link to the documents you are talking about?

Klaus

 

[FvM]

What is SMC (MDC and MDIO)?

Serial management interface, every PHY has it. Used to set parameters and read status, e.g. link speed.

Why we need TX (3:0) and RX (3:0) when we have MDIO?

Don't think so. Management interface has no connection to other pins.

 

[Bjtpower_magic]

Hi Again,
How 100MBPS achieved when we have 50 MHZ for RMII and 25MHZ for MII Interface?

 

[KlausST]

Hi,

As said, these are different interfaces.
So if one runs on 100MBits/s ... there is no need for the other to run at the same speed.

But still a 50MHz DDR single lane interface could go up to 100MBit/s.

But you completely miss that there are multiple partners on ethernet, that there is protocol overhead, making a 100MBits/s impossible.
Also you miss the FIFO / DualPortMemory between both interfaces.

Again: Different interfaces! With different features.

Klaus

 

[FvM]

How 100MBPS achieved when we have 50 MHZ for RMII and 25MHZ for MII Interface?

Not sure if you ever looked at MI and RMII interface details?

MBPS = clock frequency * number of data bits in parallel

 

[Bjtpower_magic]

Not sure if you ever looked at MI and RMII interface details?

MBPS = clock frequency * number of data bits in parallel

Hi,
Got it now.
so for MII, We have 25MHZ*4Bits:100MBPS or 2.5MHZ*4:10 MBPS
Thank you, i didnt aware about this.