Importance

Loading Importance Indicators...

Abstract

A rotating priority encoder for selecting from a number of input priority request lines that input request line which is active and which designated as having the highest priority. A mask unit selectively passes only those input request signals which have index numbers which are equal to or greater than a predetermined base-point index number. A 2N priority encoder receives two sets of input signals: L, the masked priority request signals from the mask unit, and H the original priority request signals. The masked priority signals L are given highest priority by this arrangement. The output signal of the 2N priority encoder is the index number of the lowest indexed active input request line. The base-point index number is periodically changed to designate a new input request line as having the highest priority. The masked priority request signals L are assigned the lowest numbers in a sequence of index numbers. The original priority request signals H are assigned the higher numbers in the sequence of index numbers. If the sequence of index numbers for the masked priority request signals L do not end with a number which is an integer power of two, some numbers are skipped before assigning index numbers to the H signals, beginning with a number which is an integer power of 2. For each input request line, the mask unit includes a circuit for determining whether the base-point index number exceeds a the index number of that input request number. The mask units and the 2N priority encoders are easily expanded.

Loading the Abstract Image...