USB 2.0 speed

[indi]

USB 2.0 seem to have 480Mbps speed of transfer. Can anyone explain it in detail.

USB 2.0 tranfers data is microframe (125us) compared to a frame (1ms) in USB 1.1. In a single microframe u can send 3 packets i..e 3 x 1024 = 3072 bytes.

Hence 3072 x 8 bytes in 1ms
3072 x 8 x 8 bits in 1 ms
3072 x 8 x 8 x 1000 in 1 second
...
...
it comes to 196Mbps

Then how is 480 Mbps achieved

 

[A_DOG73]

Who cares how!

I just love USB. It is so convenient. I don't know what I would do without it. :haha:

 

[Nodsu]

Look up bulk transfers.. You can fit 13 512-byte bulk packets into a microframe and you get 13*512*8*8*1000 bits per second for useful data (426Mbps)

 

[indi]

Thanks a lot, but still we are not reaching 480Mbps
Then i checked the USB 2.0 spec where I came across bulk ttransfer as 7500 bytes per micro frame which on calculation results into 480Mbps (60MBps)....but no details about data payload details or Max transfers

Look up bulk transfers.. You can fit 13 512-byte bulk packets into a microframe and you get 13*512*8*8*1000 bits per second for useful data (426Mbps)

 

[Nodsu]

That 480 is not "useful" bandwidth (who has ever heard of anyone advertising anything with its real speeds and not some arbitrary numbers? ). It is just the amount of bits that go through the wire when using the hi-speed clock rate.