How can Spartan-6 interface with 10/100 Mb/s Ethernet?

[fl]

Hi,
I read LogiCORE IP AXI Ethernet Lite MAC (v1.01.b), which says that the Ethernet
interface is with 10Mb/s 100Mb/s. On its spec, I find that the maximum clock for
Spartan xc6slx45t AXI4-lite 120 MHz (Target Fmax). I am puzzled about the two
categories numbers. 120 MHz is only marginal higher than 100 Mb/s. How can it
recover a 100 Mb/s data?
Could you explain it to me? Thanks,

 

[Russell]

Consider what happens when you go from a serial interface (like in Ethernet) to a parallel interface. If you have a 1 bit wide interface at 100 Mb/s interfacing to a 16 bit wide parallel interface, your parallel interface only needs to run at 6.25 Mb/s (100/16). As long as the module that does the serial to parallel conversion can keep up, the rest of the logic can run in parallel and can be run much slower.

On Tuesday, August 5, 2014 8:49:47 AM UTC-4, fl wrote:

Hi,

I read LogiCORE IP AXI Ethernet Lite MAC (v1.01.b), which says that the Ethernet

interface is with 10Mb/s 100Mb/s. On its spec, I find that the maximum clock for

Spartan xc6slx45t AXI4-lite 120 MHz (Target Fmax). I am puzzled about the two

categories numbers. 120 MHz is only marginal higher than 100 Mb/s. How can it

recover a 100 Mb/s data?

Could you explain it to me? Thanks,

 

[GaborSzakacs]

fl wrote:

Hi,
I read LogiCORE IP AXI Ethernet Lite MAC (v1.01.b), which says that the Ethernet
interface is with 10Mb/s 100Mb/s. On its spec, I find that the maximum clock for
Spartan xc6slx45t AXI4-lite 120 MHz (Target Fmax). I am puzzled about the two
categories numbers. 120 MHz is only marginal higher than 100 Mb/s. How can it
recover a 100 Mb/s data?
Could you explain it to me? Thanks,

The PHY interface (MII) runs at 25 MHz for a 100 Mbps link. The AXI bus
is much wider than even that interface, so it can easily deal with 1Gpbs
Ethernet. Note that the 120 MHz limit is at the AXI interface and not
the I/O side of the module.

--
Gabor