Rotating priority encoder operating by selectively masking input

Details Rotating priority encoder operating by selectively masking input Rotating priority encoder operating by selectively masking input

1989-04-25

1992-03-10

Lee, Thomas C.

Boots, shoes, and leggings

3642426, 3642428, 3642429, 3642597, 11DIG1, G06F 1318

Patent

active

050954601

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<i>, the masked priority request signals from the mask unit, and H<i> the original priority request signals. The masked priority signals L<i> 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<i> are assigned the lowest numbers in a sequence of index numbers. The original priority request signals H<i> are assigned the higher numbers in the sequence of index numbers. If the sequence of index numbers for the masked priority request signals L<i> do not end with a number which is an integer power of two, some numbers are skipped before assigning index numbers to the H<i> 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.

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Programmable Priority for Cycle Steal, C. J. Duggan, IBM Tech. Discl. Bul., vol. 19, No. 11, Apr. 1977, pp. 4354-4356.

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