US 4,546,450 AGranted

Priority determination circuit

AssigneeTokyo Shibaura Denki Kabushiki Kaisha

InventorAkira Kanuma

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Abstract

In a priority assignment circuit receiving service request signals and comprising a plurality of service enable signal transmission units for transmitting a service enable signal in accordance with a priority determined by priority signals, bypass circuits are provided each for a predetermined number of service request units. Each bypass circuit is adapted to pass the service enable signal when respective service request signals are not coupled to them from service request units.

Claims5

Dependent claims

A circuit for determining priorities among a plurality of service requesting units having different service priority levels and being connected to a data processing unit, each of said service requesting units indicating its desire for access to said data processing unit by using a different service request flag, said circuit comprising:

at least one service enable unit coupled to said plurality of service requesting units, each service enable unit having an input terminal coupled to a service enable input signal and an output terminal producing a service enable output signal,
said service enable input signal indicating whether there is any outstanding request for access to said data processing unit which has a higher service priority level than that of any of said plurality of service requesting units coupled to said service enable unit, and
said service enable output signal indicating whether any of said service requesting units coupled to said service enable unit desires access to said data processing unit or whether said service enable input signal is indicating an outstanding request for access to said data processing unit which has a higher service priority level than that of any said service requesting units,
each said service enable unit including
(a) a service enable bypassing circuit including a plurality of signal bypassing AND gates each corresponding to a different service priority level, and an OR gate having inputs connected to the output of each of said signal bypassing AND gates and having an output connected to said service enable unit output terminal, the signal bypassing AND gate corresponding to the highest service priority level having an input coupled to said service enable unit input terminal,
(b) a plurality of serially-connected service enable signal transmission units each corresponding to a different service priority level and each of said service enable transmission units including first and second NAND gates with two input terminals and an output, the output of the first NAND gate in each of said signal transmission units being coupled to a first input of the second NAND gate in that signal transmission unit and the output of the second NAND gate of each of said transmission units, except for said transmission unit corresponding to the lowest service priority level, being connected to a first input terminal of the first NAND gate in the transmission unit having the next lowest service priority level, the first NAND gate of the service enable signal transmission unit corresponding to the highest service priority level having a first input coupled to said service enable unit input terminal,
(c) a plurality of service request flip-flops each corresponding to a different signal bypassing AND gate and to the service priority level of that signal bypassing AND gate,
each of said service request flip-flops having a set terminal coupled to a different one of said service request units to receive from that unit a service request flag and each of said service request flip-flops also having first and second complementary output terminals,
said first output terminal of each service request flip-flop being connected to an input of the corresponding signal bypassing AND gate, and, except for said service request flip-flop corresponding to the lowest signal priority level, also being connected to a second input terminal of the first NAND gate in a different one of said service enable signal transmission units,
said second output terminal of each of said service request flip-flops providing a service request signal,
(d) a plurality of service request signal transmitting AND gates each corresponding to a different service request flip-flop and to the service priority level of that service request flip-flop, said service request signal transmitting AND gates each having a first input coupled either to the output of the adjacent service enable signal transmission unit or to the output of an adjacent service enable bypassing circuit, a second input terminal coupled to the service request signal of the corresponding service request flip-flop, and an output terminal,
(e) a plurality of service execution flip-flops each corresponding to a different service request signal transmitting AND gate and to the service priority level of that transmitting AND gate, each said service execution flip-flops having a set terminal connected to the output terminal of said corresponding service request signal transmitting AND gate and an output terminal providing a service execution signal, and
(f) a plurality of priority assignment flip-flops each corresponding to a different service execution flip-flop and to the service priority level of that service execution flip-flop,
each of said priority assignment flip-flops having a set terminal coupled to the service execution signal from the corresponding service execution flip-flop and each of said priority assignment flip-flops having third and fourth complementary output terminals,
said third output terminal being connected to a second input terminal of the second NAND gate in a different service enable signal transmission unit, and said fourth output terminal providing a priority signal, the priority signal of each of said priority assignment flip-flops, except the priority assignment flip-flop having the lowest priority, being connected to said signal bypassing AND gate having the next lower priority level.

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Dependencies are inferred from the claim text.

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Abstract

at least one service enable unit coupled to said plurality of service requesting units, each service enable unit having an input terminal coupled to a service enable input signal and an output terminal producing a service enable output signal,
said service enable input signal indicating whether there is any outstanding request for access to said data processing unit which has a higher service priority level than that of any of said plurality of service requesting units coupled to said service enable unit, and
said service enable output signal indicating whether any of said service requesting units coupled to said service enable unit desires access to said data processing unit or whether said service enable input signal is indicating an outstanding request for access to said data processing unit which has a higher service priority level than that of any said service requesting units,
each said service enable unit including
(a) a service enable bypassing circuit including a plurality of signal bypassing AND gates each corresponding to a different service priority level, and an OR gate having inputs connected to the output of each of said signal bypassing AND gates and having an output connected to said service enable unit output terminal, the signal bypassing AND gate corresponding to the highest service priority level having an input coupled to said service enable unit input terminal,
(b) a plurality of serially-connected service enable signal transmission units each corresponding to a different service priority level and each of said service enable transmission units including first and second NAND gates with two input terminals and an output, the output of the first NAND gate in each of said signal transmission units being coupled to a first input of the second NAND gate in that signal transmission unit and the output of the second NAND gate of each of said transmission units, except for said transmission unit corresponding to the lowest service priority level, being connected to a first input terminal of the first NAND gate in the transmission unit having the next lowest service priority level, the first NAND gate of the service enable signal transmission unit corresponding to the highest service priority level having a first input coupled to said service enable unit input terminal,
(c) a plurality of service request flip-flops each corresponding to a different signal bypassing AND gate and to the service priority level of that signal bypassing AND gate,
each of said service request flip-flops having a set terminal coupled to a different one of said service request units to receive from that unit a service request flag and each of said service request flip-flops also having first and second complementary output terminals,
said first output terminal of each service request flip-flop being connected to an input of the corresponding signal bypassing AND gate, and, except for said service request flip-flop corresponding to the lowest signal priority level, also being connected to a second input terminal of the first NAND gate in a different one of said service enable signal transmission units,
said second output terminal of each of said service request flip-flops providing a service request signal,
(d) a plurality of service request signal transmitting AND gates each corresponding to a different service request flip-flop and to the service priority level of that service request flip-flop, said service request signal transmitting AND gates each having a first input coupled either to the output of the adjacent service enable signal transmission unit or to the output of an adjacent service enable bypassing circuit, a second input terminal coupled to the service request signal of the corresponding service request flip-flop, and an output terminal,
(e) a plurality of service execution flip-flops each corresponding to a different service request signal transmitting AND gate and to the service priority level of that transmitting AND gate, each said service execution flip-flops having a set terminal connected to the output terminal of said corresponding service request signal transmitting AND gate and an output terminal providing a service execution signal, and
(f) a plurality of priority assignment flip-flops each corresponding to a different service execution flip-flop and to the service priority level of that service execution flip-flop,
each of said priority assignment flip-flops having a set terminal coupled to the service execution signal from the corresponding service execution flip-flop and each of said priority assignment flip-flops having third and fourth complementary output terminals,
said third output terminal being connected to a second input terminal of the second NAND gate in a different service enable signal transmission unit, and said fourth output terminal providing a priority signal, the priority signal of each of said priority assignment flip-flops, except the priority assignment flip-flop having the lowest priority, being connected to said signal bypassing AND gate having the next lower priority level.

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