Importance

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Abstract

One embodiment of the present invention provides a method for selectively encoding bus grant lines to reduce I/O pin requirements. The method includes receiving a number of grant lines emanating from a bus arbitration circuit and encoding the grant lines into a smaller number of encoded grant lines. The method selects outputs from between the encoded grant lines and a first subset of the grant lines. These outputs are driven off of a semiconductor chip through a number of output pins. During a first mode of operation, the first subset of grant lines is selected to be driven through the output pins. During a second mode of operation, the encoded grant lines are selected to driven through the output pins. In a variation on the above embodiment, the method additionally receives a number of bus request lines. These request lines are divided into a first subset and a second subset. The first subset of request lines is received through a number of input pins from off of the semiconductor chip. During the first mode of operation, the second subset of request lines is received from off of the semiconductor chip through a number of I/O pins and bi-directional buffers into the bus arbitration circuit. This first mode of operation allows more request lines to be used in conjunction with the plurality of encoded grant lines. During the second mode of operation, the second subset of bus grant lines feeds from the bus arbitration circuit through the bi-directional buffers and I/O pins and off of the semiconductor chip. This second mode of operation allows more pins to be used for grant lines when grant lines are not encoded.

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First Claim