Electronic digital logic circuitry – Signal sensitivity or transmission integrity – Bus or line termination
Reexamination Certificate
1999-05-21
2001-02-13
Tokar, Michael (Department: 2819)
Electronic digital logic circuitry
Signal sensitivity or transmission integrity
Bus or line termination
C326S026000, C326S086000
Reexamination Certificate
active
06188238
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to buses and more particularly to termination of buses for use in information processing systems.
2. Description of the Related Art
In computer and information processing systems, various integrated circuit chips communicate digitally with each other over a common bus. The signal frequency at which this communication occurs can limit the performance of the overall system. Thus, the higher the communication frequency, the better. The maximum frequency at which a system communicates is a function not only of the time that it takes for the electromagnetic wavefronts to propagate on the bus from one chip to another, but also of the time required for the signals to settle to levels that can be recognized reliably at the receiving bus nodes as being high or low, referred to as the settling time.
The length of the settling time is a function of the amount of reflection and ringing that occurs on the transmission line. The more effective the termination of a bus system, the smaller the effects of reflection and ringing in the system and the shorter the overall settling time of the signal.
SUMMARY OF THE INVENTION
A method for terminating signals in an information handling system comprises includes providing a plurality of resistance elements, providing at least three transmission lines each having a characteristic impedance, each of the transmission lines having a first end, each of the first ends being coupled together through said resistance elements, and a second end, and providing a plurality of drivers equaling the number of transmission lines in the plurality of transmission lines, each driver coupled to a second end of a different one of the transmission lines, each driver comprising a pull-down circuit having a pull-down resistance matched to the characteristic impedance of one of the lines, and a pull-up circuit having a pull-up resistance corresponding to the number of second ends. The method further includes providing at least one receiver circuit coupled to a second end of one of the transmission lines, designating one of the drivers as an active driver, and designating each driver in the plurality of drivers other than the active driver as a terminating driver. Finally, the method includes causing each terminating driver to be configured in a nonactive pull-down terminating configuration, and causing the active driver to drive a signal onto the transmission line to which the active driver is connected.
REFERENCES:
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patent: 6084424 (2000-07-01), Gasparik
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Le Don Phu
Sierra Patent Group Ltd.
Sun Microsystems. Inc.
Tokar Michael
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