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Diffstat (limited to 'decoders/usb/__init__.py')
| -rw-r--r-- | decoders/usb/__init__.py | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/decoders/usb/__init__.py b/decoders/usb/__init__.py index 068cadf..77b58d1 100644 --- a/decoders/usb/__init__.py +++ b/decoders/usb/__init__.py @@ -18,5 +18,27 @@ ## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA ## +''' +USB (full-speed) protocol decoder. + +Full-speed USB signalling consists of two signal lines, both driven at 3.3V +logic levels. The signals are DP (D+) and DM (D-), and normally operate in +differential mode. +The state where DP=1,DM=0 is J, the state DP=0,DM=1 is K. +A state SE0 is defined where DP=DM=0. This common mode signal is used to +signal a reset or end of packet. + +Data transmitted on the USB is encoded with NRZI. A transition from J to K +or vice-versa indicates a logic 0, while no transition indicates a logic 1. +If 6 ones are transmitted consecutively, a zero is inserted to force a +transition. This is known as bit stuffing. Data is transferred at a rate +of 12Mbit/s. The SE0 transmitted to signal an end-of-packet is two bit +intervals long. + +Details: +https://en.wikipedia.org/wiki/USB +http://www.usb.org/developers/docs/ +''' + from .usb import * |