TAP Controller
MOTOROLA
JTAG Port
17-21
Preliminary
17
3. When the 56800E TAP is selected, the EOnCE module is selected by shifting the
ENABLE_EOnCE instruction.
4. The EOnCE module registers and commands are read and written through the
JTAG pins using the shift-DR-scan path.
Asserting the JTAG’s TRST pin asynchronously forces the JTAG state machine into the
test-logic-reset state.
17.8.1 Operation
All state transitions of the TAP Controller occur based on the value of TMS at the time of
a rising edge of TCK. Actions of the instructions occur on the falling edge of TCK in each
17.8.1.1 Test Logic Reset (pstate = F)
During Test-Logic-Reset all JTAG test logic is disabled so the chip can operate in a
normal mode. This is achieved by initializing the Instruction Register (IR) with the
IDCODE instruction. By holding TMS high for five rising edges of TCK, the device will
always remain in Test-Logic-Reset no matter what state the TAP Controller was in
previously.
17.8.1.2 Run-Test-Idle (pstate = C)
Run-Test-Idle is a controller state between scan operations. When EOnCE is entered, the
controller will remain in the Run-Test-Idle mode as long as TMS is held low. When TMS
is high and a rising edge of TCK occurs, the controller moves to the Select-DR state.
17.8.1.3 Select Data Register (pstate = 7)
The Select-DR state is a temporary state. In this state, all Test Data registers selected by
the current instruction retains their previous states. If TMS is held low and a rising edge of
TCK occurs when the controller is in this state, the controller moves into the Capture-DR
state and a scan sequence for the selected test date register is initiated. If TMS is held high
and a rising edge of TCK occurs, the controller moves to the Select-IR state.
17.8.1.4 Select Instruction Register (pstate = 4)
The Select-IR state is a temporary state. In this state, all Test Data registers selected by the
current instruction retain their previous states. If TMS is held low and a rising edge of
TCK occurs when the controller is in this state, the controller moves into the Capture-IR
state and a scan sequence for the instruction register is initiated. If TMS is held high and a
rising edge of TCK occurs, the controller moves to the Test-Logic-Reset state.