DS3153N datasheet(33/60 Pages) DALLAS

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DS3151/DS3152/DS3153/DS3154 Single/Dual/Triple/Quad DS3/E3/STS-1 LIUs

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12.2 JTAG TAP Controller State Machine Description

This section discusses the operation of the TAP controller state machine. The TAP controller is a finite state

machine that responds to the logic level at JTMS on the rising edge of JTCLK. Each of the states denoted in Figure

12-2 are described in the following pages.

Figure 12-2. JTAG TAP Controller State Machine

Test-Logic-Reset. Upon device power-up, the TAP controller starts in the Test-Logic-Reset state. The instruction

Run-Test-Idle. Run-Test-Idle is used between scan operations or during specific tests. The instruction and test

registers remain idle.

Select-DR-Scan. All test registers retain their previous state. With JTMS low, a rising edge of JTCLK moves the

controller into the Capture-DR state and initiates a scan sequence. JTMS high moves the controller to the Select-

IR-SCAN state.

Capture-DR. Data can be parallel loaded into the test data registers selected by the current instruction. If the

instruction does not call for a parallel load or the selected register does not allow parallel loads, the test register

remains at its current value. On the rising edge of JTCLK, the controller goes to the Shift-DR state if JTMS is low or

to the Exit1-DR state if JTMS is high.

Test-Logic-Reset

Run-Test/Idle

Select

DR-Scan

Capture-DR

Shift-DR

Exit1- DR

Pause-DR

Exit2-DR

Update-DR

Select

IR-Scan

Capture-IR

Shift-IR

Exit1-IR

Pause-IR

Exit2-IR

Update-IR

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