DS2155 datasheet(201/238 Pages) DALLAS

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DS2155

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Select-IR-Scan

All test registers retain their previous state. The instruction register remains unchanged during this state.

With JTMS LOW, a rising edge on JTCLK moves the controller into the Capture-IR state and initiates a

scan sequence for the instruction register. JTMS HIGH during a rising edge on JTCLK puts the controller

back into the Test-Logic-Reset state.

Capture-IR

The Capture-IR state is used to load the shift register in the instruction register with a fixed value. This

value is loaded on the rising edge of JTCLK. If JTMS is HIGH on the rising edge of JTCLK, the

controller enters the Exit1-IR state. If JTMS is LOW on the rising edge of JTCLK, the controller enters

the Shift-IR state.

Shift-IR

In this state, the shift register in the instruction register is connected between JTDI and JTDO and shifts

data one stage for every rising edge of JTCLK toward the serial output. The parallel register and all test

registers remain at their previous states. A rising edge on JTCLK with JTMS HIGH moves the controller

to the Exit1-IR state. A rising edge on JTCLK with JTMS LOW keeps the controller in the Shift-IR state

while moving data one stage through the instruction shift register.

Exit1-IR

A rising edge on JTCLK with JTMS LOW puts the controller in the Pause-IR state. If JTMS is HIGH on

the rising edge of JTCLK, the controller enters the Update-IR state and terminates the scanning process.

Pause-IR

Shifting of the instruction shift register is halted temporarily. With JTMS HIGH, a rising edge on JTCLK

puts the controller in the Exit2-IR state. The controller remains in the Pause-IR state if JTMS is LOW

during a rising edge on JTCLK.

Exit2-IR

A rising edge on JTCLK with JTMS LOW puts the controller in the Update-IR state. The controller loops

back to Shift-IR if JTMS is HIGH during a rising edge of JTCLK in this state.

Update-IR

The instruction code shifted into the instruction shift register is latched into the parallel output on the

falling edge of JTCLK as the controller enters this state. Once latched, this instruction becomes the

current instruction. A rising edge on JTCLK with JTMS LOW puts the controller in the Run-Test-Idle

state. With JTMS HIGH, the controller enters the Select-DR-Scan state.

DS2155 Datasheet(PDF) 201 Page - Dallas Semiconductor