Structure and method for SDRAM dynamic self refresh entry and exit using JTAG
First Claim
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1. A circuit test method comprising:
- asserting a first signal to a memory controller unit from a test logic circuit to indicate a start of the circuit test;
asserting a second signal from said memory controller unit to said test logic circuit to indicate that said memory controller unit has finished the current memory access;
placing of a dynamic memory coupled to said memory controller unit into a self refresh mode in response to both said first signal and said second signal being asserted; and
testing a circuit while said dynamic memory is in said self refresh mode, said self-refresh mode being used to preserve pretest contents of said dynamic memory during said testing.
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Abstract
JTAG test logic and a memory controller place an SDRAM in a self refresh mode prior to beginning JTAG testing. The memory controller can complete a current memory access and otherwise prepare for the JTAG test. During the JTAG test, self refresh mode operation of the SDRAM retains data without the need for a clock signal or refresh signals which are suspended for the JTAG test. Accordingly, after the JTAG test, circuit operation can continue without reinitializing data in the SDRAM.
81 Citations
16 Claims
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1. A circuit test method comprising:
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asserting a first signal to a memory controller unit from a test logic circuit to indicate a start of the circuit test; asserting a second signal from said memory controller unit to said test logic circuit to indicate that said memory controller unit has finished the current memory access; placing of a dynamic memory coupled to said memory controller unit into a self refresh mode in response to both said first signal and said second signal being asserted; and testing a circuit while said dynamic memory is in said self refresh mode, said self-refresh mode being used to preserve pretest contents of said dynamic memory during said testing. - View Dependent Claims (2, 3, 4, 5, 16)
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6. A circuit comprising:
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a memory controller; a test logic coupled to said memory controller wherein prior to a circuit test, said test logic asserts a first signal that indicates to said memory controller that a system clock bypass is being requested and said memory controller asserts a second signal to said test logic when a current memory access operation is complete; and a dynamic memory capable of operating in self refresh mode coupled to said memory controller, wherein said memory controller places said dynamic memory into said self refresh mode in response to said first signal and said second signal being asserted, said self refresh mode being used to preserve pretest contents of said dynamic memory during said circuit test. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15)
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Specification