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Message
From: "Ravi Rajaraman" <ravi_prr2000@h...>
Date: Thu, 13 Nov 2003 15:00:38 -0800
Subject: Re: [usb] sync packet in full speed mode and low speed mode
Hi Tom,
The better way to view a J or K state for full and low speed is as follows :
Full speed :
------------
J state ===> D + = '1' & D- = '0';
K state ===> D + = '0' & D- = '1';
Low Speed :
---------------
J state ===> D + = '0' & D- = '1';
K state ===> D + = '1' & D- = '0';
For Full speed data comes along D + lines which is what we decode. ie for
sync the following sequence will be followed.
D + = '0'
D + = '1';
D + = '0'; and goes on till sync ends.
But for a low speed the data comes on D - lines and we should view it and
decode it separately for each speeds.
D - = '0'
D - = '1';
D - = '0'; and goes on till sync ends.
Dont try visualising it from D + point alone.If that is so then what you
said might be true.Try visualising things from the data line point ie which
line takes data.That would make things easier for you.
Regards,
Ravi
----- Original Message -----
From: <tomko81@h...>
To: <usb@o...>
Sent: Wednesday, November 12, 2003 6:07 PM
Subject: [usb] sync packet in full speed mode and low speed mode
> Hi everyone,
>
> It seems K state mean differental logic'0' in full speed , logic
'1' in
> slow speed, also for SOP in USB, it need to change from IDLE state to K
> state.
> My question is that for the sync packet"00000001"(LSB at the
> left hand side) after the SOP,after the NRZI, is it become "01010100" for
> full speed but become " 10101011" for slow speed? so that it can satisfy
> the SOP condition due to the difference of K state in two mode.
>
> The USB spec. only give one example and it haven't mention clearly
> it is full speed or low speed. Please tell me whether i am right or wrong.
> Thank you very much.
>
>
>
> TOM
>
>
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