Universal serial bus transceiver shortcut protection

Details Universal serial bus transceiver shortcut protection Universal serial bus transceiver shortcut protection

1999-12-29

2004-06-01

Myers, Paul R. (Department: 2181)

Error detection/correction and fault detection/recovery

Data processing system error or fault handling

Reliability and availability

Reexamination Certificate

active

06745342

ABSTRACT:

RESERVATION OF COPYRIGHT
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records available to the public, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to bus interfaces, and in particular, to a system and method for providing short circuit protection for a Universal Serial Bus (USB) interface.
2. Description of the Related Art
The Universal Serial Bus (USB) is a bi-directional, isochronous, dynamically attachable serial interface providing two wire point to point signaling. Signals are differentially driven at a bit rate of 12 megabits per second.
An exemplary Universal Serial Bus interface is shown in FIG.
1
. As shown, the interface includes a USB transceiver
102
, typically embodied as an integrated circuit. At least four contacts are provided at a chip boundary
104
. These are VDD (5 V)
106
, VSS (0 V)
112
, and the data ports DPLS
108
and DMNS
110
(0-3.3 V).
A short circuit of DPLS or DMNS to VDD or VSS while the bus is being driven could damage the transceiver. Accordingly, the Universal Serial Bus Specification Version 1.1 requires that the transceiver connected to DPLS and DMNS must resist a short circuit of DPLS and DMNS to VDD or VSS.
SUMMARY OF THE INVENTION
These and other drawbacks in the prior art are overcome in large part by transceiver shortcut protection according to the present invention. A Universal Serial Bus interface according to one implementation includes a USB device controller coupled by way of a shortcut protection circuit to a USB transceiver. The shortcut protection circuit compares the driven DPLS and DMNS signals from the USB transceiver with TxDPLS and TxDMNS, the transmitted signals from the USB device controller. If a difference is detected between TxDPLS and DPLS, or between TxDMNS and DMNS, the transmission is disabled.
A shortcut protection unit according to one implementation includes a comparison circuit and a disable circuit. The comparison circuit is embodied as a state machine for periodically comparing the TxDPLS and DPLS signals, and the TxDMNS and DMNS signals. If different signal levels are detected, then the state machine provides an output to the disable circuit. In turn, the disable circuit turns off the USB transceiver's transmit enable.


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Anonymous, “Data Sensing Cut-Off Scheme,”IBM Technical Disclosure Bulletin, 1985, 28(3):1262-1263.

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