Electronic digital logic circuitry – Signal sensitivity or transmission integrity – Bus or line termination
Reexamination Certificate
1999-05-25
2001-08-14
Tokar, Michael (Department: 2819)
Electronic digital logic circuitry
Signal sensitivity or transmission integrity
Bus or line termination
C326S057000, C326S086000, C710S108000
Reexamination Certificate
active
06275062
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
An information handling system includes a plurality of transmission lines coupled together at one end and having a characteristic impedance, a driver circuit coupled to one of the transmission lines, and at least one receiver circuit coupled to the transmission lines. At least one driver circuit includes pull-up and pull-down circuits each having output resistances. The parallel combination of the pull-up and pull-down resistances matches the characteristic impedance of the transmission line. When the driver is used to terminate the transmission line, the pull-up and pull down circuits are enabled at approximately the same time, thus terminating the line. On-chip terminators may alternatively be used for termination, the terminators either including pull-up and pull-down circuits substantially similar to those described for the drivers, or may include a single resistance tied to a voltage other than an upper or lower rail. A method for managing the information handling system described above includes terminating each node by causing either an on-chip terminator or a driver to go into a terminating mode, thus causing the termination of the line using an output resistance that matches the characteristic impedance of the transmission line.
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Chang Daniel D.
Sierra Patent Group
Sun Microsystems Inc.
Tokar Michael
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