Single-chip microcomputer using adjustable timing to fetch data from an external memory
First Claim
1. A single-chip microcomputer having input terminals and output terminals, in combination with an external ROM having input terminals that are connected to the output terminals of the single-chip microcomputer and having output terminals that are connected to the input terminals of the single-chip microcomputer,wherein the external ROM stores instruction data;
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an internal ROM which stores instruction data;
an internal/external switching signal generation circuit for generating an internal/external switching signal having a first digital level or a second digital level;
means for reading instruction data out of the internal and external ROMs;
a selector to select either instruction data that has been read out of the internal ROM or instruction data that has been read out of the external ROM according to the level of the internal/external switching signal;
an instruction register to receive the instruction data selected by the selector, the selected instruction data being fetched into the instruction register by a fetch control signal; and
means for emitting the fetch control signal to the instruction register at a timing which depends on the level of the internal/external switching signal, the means for emitting comprising a data fetch signal generation circuit which generates a data fetch signal, means connected to one of the output terminals of the single-chip microcomputer for generating a further signal, and means responsive to the internal/external switching signal for passing either the data fetch signal or the further signal to the instruction register as the fetch control signal.
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Accused Products
Abstract
It is an object of the present invention to provide a one-chip microcomputer which permits the access time for an external memory to be equal to that for an internal memory. The one-chip microcomputer 10 includes an internal ROM 11, control circuit 12, output terminals 13, input terminals 14, control circuit 15, selector 16, instruction register 17, delay circuit 18, and fetch control signal select gate 19. For selection of the external ROM 30, a control arrangement 20 and a delay circuit 18 are employed in one embodiment to adjust the time at which ROM data is fetched by the instruction register 17, based on the delay time for accessing the external ROM 30.
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Citations
13 Claims
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1. A single-chip microcomputer having input terminals and output terminals, in combination with an external ROM having input terminals that are connected to the output terminals of the single-chip microcomputer and having output terminals that are connected to the input terminals of the single-chip microcomputer,
wherein the external ROM stores instruction data; - and
wherein the single-chip microcomputer comprises; an internal ROM which stores instruction data; an internal/external switching signal generation circuit for generating an internal/external switching signal having a first digital level or a second digital level; means for reading instruction data out of the internal and external ROMs; a selector to select either instruction data that has been read out of the internal ROM or instruction data that has been read out of the external ROM according to the level of the internal/external switching signal; an instruction register to receive the instruction data selected by the selector, the selected instruction data being fetched into the instruction register by a fetch control signal; and means for emitting the fetch control signal to the instruction register at a timing which depends on the level of the internal/external switching signal, the means for emitting comprising a data fetch signal generation circuit which generates a data fetch signal, means connected to one of the output terminals of the single-chip microcomputer for generating a further signal, and means responsive to the internal/external switching signal for passing either the data fetch signal or the further signal to the instruction register as the fetch control signal. - View Dependent Claims (2)
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3. A single-chip microcomputer which is selectively connectable to an external storage means for outputting data, said single-chip microcomputer comprising:
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an output terminal, the output terminal being selectively connectable to the external storage means; an internal storage means for outputting data; an internal/external switching signal generation circuit for generating an internal/external switching signal having a first digital level or a second digital level; a selector to select either data that has been output by the internal storage means or data that has been output by the external storage means according to the level of the internal/external switching signal; and means for emitting a fetch control signal for fetching the selected data from the selector at a timing which depends on the level of the internal/external switching signal, the means for emitting comprising a data fetch signal generation circuit which generates a data fetch signal, means connected to the output terminal for generating a further signal, and means responsive to the internal/external switching signal for selecting either the data fetch signal or the further signal for use as the fetch control signal. - View Dependent Claims (4)
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5. A single-chip microcomputer which is selectively connectable to an external storage means for outputting data, said single-chip microcomputer comprising:
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an output terminal, the output terminal being selectively connectable to the external storage means; an internal storage means for outputting data; an internal/external switching signal generation circuit for generating an internal/external switching signal having a first digital level or a second digital level; a selector to select either data that has been output by the internal storage means or data that has been output by the external storage means according to the level of the internal/external switching signal; an instruction register to receive the data selected by the selector, the selected data being latched into the instruction register by a fetch control signal; means for emitting the fetch control signal to the instruction register at a timing which depends on the level of the internal/external signal, the means for emitting comprising a data fetch signal generation circuit which generates a data fetch signal, means connected to the output terminal for generating a further signal, and means responsive to the internal/external switching signal for passing either the data fetch signal or the further signal to the instruction register as the fetch control signal. - View Dependent Claims (6)
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7. A single-chip microcomputer which is capable of executing first instructions and executing second instructions that are stored in an external storage unit that is connectable to the single-chip microcomputer, comprising:
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an internal storage unit for storing the first instructions; a program counter; a first generation circuit for emitting a strobe signal; first means for conveying the strobe signal and an address emitted by the program counter to the internal storage unit and to the external storage unit, the address and the strobe signal reaching the internal storage unit and then reaching the external storage unit after a delay; an instruction register; second means for selecting either a first instruction read out of the internal storage unit or a second instruction read out of the external storage unit in response to the address and the strobe signal, and for conveying the selected instruction to the instruction register; a second generation circuit for emitting a fetch signal after the address and the strobe signal have been emitted; and third means for conveying the fetch signal to the instruction register so that the instruction register latches the selected instruction into the instruction register a first period of time after the fetch signal was emitted, if the selected instruction is a first instruction, and so that the instruction register latches the selected instruction into the instruction register a second period of time after the fetch signal was emitted, if the selected instruction is a second instruction, the second period of time being longer than the first period of time to compensate for the delay. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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Specification