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TAP Controller

13.3 TAP Controller

The TAP controller is a synchronous finite state machine that contains 16 states, as illustrated in

Figure 13-5. The TAP controller responds to changes at the TMS and TCK signals. Transitions from one state to another occur on the rising edge of TCK. The value shown adjacent to each state transition in this figure represents the signal present at TMS at the time of a rising edge at TCK. The TDO pin remains in the high impedance state except during the Shift-DR or Shift-IR controller states. In these controller states, TDO is updated on the falling edge of TCK. TDI is sampled on the rising edge of TCK.

 

 

 

 

 

 

Shift-DR-Scan Path

Shift-IR-Scan Path

 

 

 

 

 

 

for Data

for Instructions

1

Test-Logic-Reset

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

1

1

 

Run-Test/Idle

 

 

Select-DR-Scan

 

Select-IR-Scan

 

 

 

 

 

 

0

 

0

 

0

 

 

1

 

1

 

Capture-DR

 

Capture-IR

 

0

 

0

 

Shift-DR

 

Shift-IR

 

1

0

1

0

 

 

 

1

 

1

Exit1-DR

 

Exit1-IR

 

0

 

0

 

Pause-DR

 

Pause-IR

 

1

0

1

0

 

 

0

 

0

 

Exit2-DR

 

Exit2-IR

 

1

 

1

 

Update-DR

 

Update-IR

 

1

0

1

0

 

 

 

AA0114

Figure 13-5. TAP Controller State Diagram

 

JTAG Port

13-13

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