DS31256 datasheet(165/183 Pages) MAXIM

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DS31256 256-Channel, High-Throughput HDLC Controller

165 of 183

Test-Logic-Reset. The TAP controller is in the Test-Logic-Reset state upon DS31256 power-up. The

instruction register contains the IDCODE instruction. All system logic on the DS31256 operates

normally.

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 it goes to the Exit1-DR state if JTMS is high.

Shift-DR. The test data register selected by the current instruction is connected between JTDI and JTDO

and shifts data one stage toward its serial output on each rising edge of JTCLK. If a test register selected

by the current instruction is not placed in the serial path, it maintains its previous state.

Exit1-DR. While in this state, a rising edge on JTCLK with JTMS high puts the controller in the Update-

DR state, which terminates the scanning process. A rising edge on JTCLK with JTMS low puts the

controller in the Pause-DR state.

Pause-DR. Shifting of the test registers is halted while in this state. All test registers selected by the

current instruction retain their previous states. The controller remains in this state while JTMS is low. A

rising edge on JTCLK with JTMS high puts the controller in the Exit2-DR state.

Exit2-DR. While in this state, a rising edge on JTCLK with JTMS high puts the controller in the Update-

DR state and terminates the scanning process. A rising edge on JTCLK with JTMS low enters the Shift-

DR state.

Update-DR. A falling edge on JTCLK while in the Update-DR state latches the data from the shift

because of changes in the shift register. 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.

Select-IR-Scan. All test registers retain their previous states. 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 as

DS31256 Folha de dados(PDF) 165 Page - Maxim Integrated Products