Electronic digital logic circuitry – Signal sensitivity or transmission integrity – Bus or line termination
Patent
1996-06-21
1998-07-14
Santamauro, Jon
Electronic digital logic circuitry
Signal sensitivity or transmission integrity
Bus or line termination
326 21, 326 86, H03K 1716
Patent
active
057810281
ABSTRACT:
A bidirectional universal serial bus (USB) includes switched terminations that are selectively activated to terminate the receiving end of the data bus in its characteristic impedance. The USB includes a twisted pair data cable that permits bidirectional data communication between a USB interface in a computer and a USB peripheral device. To control the bidirectional communication, the USB defines a transmit mode and a receive mode. Each end of the twisted pair data cable includes a selectively activatable switch termination that terminates the twisted pair data cable in its characteristic impedance when selectively activated. When the USB peripheral device is in the receive mode, the switched termination within the USB peripheral device is selectively activated so that the twisted pair data cable is terminated in its characteristic impedance. This reduces ringing and electromagnetic (EM) radiation on the twisted pair data cable. The switched termination within the USB interface in the computer is not activated when the USB interface is in the transmit mode. If the USB peripheral is placed in the transmit mode, and the USB interface in the computer is placed in the receive mode, the switched termination within the USB interface in the computer is selectively activated while the switched termination within the USB peripheral is placed in an inactive state. In this manner, the twisted pair data cable is always terminated in the proper impedance only at the receiving end.
REFERENCES:
patent: 5457406 (1995-10-01), Takada et al.
patent: 5528168 (1996-06-01), Kleveland
patent: 5578939 (1996-11-01), Beers et al.
patent: 5604450 (1997-02-01), Borkar et al.
patent: 5635852 (1997-06-01), Wallace
Microprocessor and Microcomputer Standards Commitee of the IEEE Computer Society (Sponsor), IEEE Standard for a High Performance Serial Bus, The Institute of Electrical and Electronics Engineers, Inc., New York 1996.
Serial Bus Specification Revision 0.8; Compaq Computer Corporation, Digital Equipment Corporation, Intel Corporation, Microsoft Corpporation, NEC Corporation, and Northern Telecom; Dec. 30, 1994.
Microsoft Corporation
Santamauro Jon
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