Semiconductor memory with multiple clocking for test mode entry
First Claim
1. An integrated circuit having a normal operating mode, and having a special operating mode enabled by an enable signal, comprising:
- a first terminal for receiving pulses of a mode initiate signal indicating entry into a special operating mode; and
an enable circuit, having an input coupled to said first terminal, and having an output for presenting said enable signal responsive to receipt, at said first terminal, of a plurality of pulses of said mode initiate signal, wherein said enable circuit comprises sequential logic for storing a state indicating the receipt of a single pulse of said mode initiate signal and for not presenting said enable signal responsive to receipt, at said first terminal, of a signal pulse of said mode initiate signal.
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Accused Products
Abstract
An integrated circuit having a normal operating mode and a special operating mode, such as a special test mode, is disclosed. The special test mode is enabled by a series of signals, such as overvoltage excursions at a terminal, rather than by a single such excursion, so that it is less likely that the special test mode is entered inadvertently, such as due to noise or power-down and power-up of the device. The circuit for enabling the test mode includes a series of D-type flip-flops, each of which are clocked upon detection of the overvoltage condition together with a particular logic level applied at another terminal; multiple series of flip-flops may be provided for multiple special test modes. Additional features include the provision of a power-on reset circuit which locks out the entry into the test mode during power-up of the device. Acknowledgment of the entry into test mode is provided by the presentation of a low impedance at output terminals while the device is not enabled; chip enable of the device causes the device to exit the test mode. Once in test mode, the output enable terminal of the device can provide a chip enable function.
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Citations
21 Claims
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1. An integrated circuit having a normal operating mode, and having a special operating mode enabled by an enable signal, comprising:
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a first terminal for receiving pulses of a mode initiate signal indicating entry into a special operating mode; and an enable circuit, having an input coupled to said first terminal, and having an output for presenting said enable signal responsive to receipt, at said first terminal, of a plurality of pulses of said mode initiate signal, wherein said enable circuit comprises sequential logic for storing a state indicating the receipt of a single pulse of said mode initiate signal and for not presenting said enable signal responsive to receipt, at said first terminal, of a signal pulse of said mode initiate signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for enabling a special operating mode of a circuit, comprising:
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receiving a plurality of mode initiate pulses at a first terminal of said circuit; and generating a special mode enable signal responsive to receipt of said plurality of mode initiate pulses, wherein said special mode enable signal is not generated responsive to receipt of a single one of said plurality of mode initiate pulses. - View Dependent Claims (13, 15, 16)
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14. The method of clam 13, wherein each of said plurality of mode initiate pulses comprises a signal having an amplitude outside of said range.
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17. A circuit for enabling a special operating mode, comprising:
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a first terminal; a plurality of latches connected in series with one another, a first one of said plurality of latches having a known logic state connected to its data input, and a last one of said plurality of latches generating an enable output at its output; a clocking circuit coupled to said first terminal and to clock inputs of said plurality of latches, for presenting a clock signal to said plurality of latches responsive to receipt of a mode initiate signal at said first terminal. - View Dependent Claims (18, 19, 20, 21)
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Specification