Maxim DS21Q55 Select-IR-Scan, Capture-IR, Shift-IR, Exit1-IR, Pause-IR, Exit2-IR, Update-IR

Product Preview DS21Q55

Select-IR-Scan

All test registers retain their previous state. The instruction register will remain unchanged during this state. With JTMS LOW, a rising edge on JTCLK moves the controller into the capture-IR state and will initiate 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 will enter the exit1-IR state. If JTMS is LOW on the rising edge of JTCLK, the controller will enter 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 towards the serial output. The parallel register as well as all test registers remain at their previous states. A rising edge on JTCLK with JTMS HIGH will move the controller to the exit1-IR state. A rising edge on JTCLK with JTMS LOW will keep the controller in the shift-IR state while moving data one stage thorough the instruction shift register.

Exit1-IR

A rising edge on JTCLK with JTMS LOW will put the controller in the pause-IR state. If JTMS is HIGH on the rising edge of JTCLK, the controller will enter the update-IR state and terminate the scanning process.

Pause-IR

Shifting of the instruction shift register is halted temporarily. With JTMS HIGH, a rising edge on JTCLK will put the controller in the exit2-IR state. The controller will remain 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 will put the controller in the update-IR state. The controller will loop 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, will put the controller in the run-test-idle state. With JTMS HIGH, the controller will enter the select-DR-scan state.

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