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DS33R11 Ethernet Mapper with Integrated T1/E1/J1 Transceiver
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14.1 JTAG TAP Controller State Machine Description
This section covers the details on the operation of the Test Access Port (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.
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.
See
Figure 14-2 for a diagram of the state machine operation.
Test-Logic-Reset
Upon power up, the TAP Controller is in the Test-Logic-Reset state. The Instruction register will contain the
IDCODE instruction. All system logic of the device will operate normally.
Run-Test-Idle
The Run-Test-Idle is used between scan operations or during specific tests. The Instruction register and test
registers will 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 will initiate a scan sequence. JTMS HIGH during a rising edge on JTCLK moves the
controller to the Select-IR-Scan state.
Capture-DR
Data may 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 will remain at its
current value. On the rising edge of JTCLK, the controller will go to the Shift-DR state if JTMS is LOW or it will go
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 will shift data
one stage towards 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 will maintain its previous state.
Exit1-DR
While in this state, a rising edge on JTCLK will put the controller in the Update-DR state, which terminates the
scanning process, if JTMS is HIGH. A rising edge on JTCLK with JTMS LOW will put 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 will
retain their previous state. The controller will remain in this state while JTMS is LOW. A rising edge on JTCLK
with JTMS HIGH will put the controller in the Exit2-DR state.
Exit2-DR
A rising edge on JTCLK with JTMS HIGH while in this state will put the controller in the Update-DR state and
terminate the scanning process. A rising edge on JTCLK with JTMS LOW will enter the Shift-DR state.