Test mode entrance through clocked addresses
First Claim
1. A method, comprising generating a test mode enable signal in an integrated circuit device by propagating a logic signal through a series of key stages in response to a number of keys of a key sequence and a clock signal.
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Abstract
A robust system for entering a test mode in an integrated circuit, for example, a memory device, greatly eliminates the probability of unintentionally entering the test mode, yet provides a system of access through a precise address and control pin sequence. By using an existing control pin present on the integrated circuit as a clock signal input for a series of latches, the present scheme sets up a number of address with predetermined values in order to create a key that is correct only if all the addresses are at the correct values. The key, combined with the clock signal input, allows a test mode enable signal to pass through each latch in a series. By further requiring that the address sequence for the key be input during an otherwise "illegal" operation for the integrated circuit, the present scheme further ensures that unintentional entry to the test mode is avoided.
84 Citations
21 Claims
- 1. A method, comprising generating a test mode enable signal in an integrated circuit device by propagating a logic signal through a series of key stages in response to a number of keys of a key sequence and a clock signal.
- 10. A method, comprising propagating a test mode enable signal through a series of clocked key stages in an integrated circuit device in response to a common clock signal and a series of unique key signals, each configured to activate a corresponding one of the clocked key stages.
- 14. An integrated circuit, comprising test mode enable circuitry responsive to a series of key signals each configured to activate a corresponding one of a number of key stages of the test mode enable circuitry and a common clock signal for the key stages.
Specification