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CHAPTER 6 JTAG BOUNDARY SCAN
User’s Manual S14054EJ4V0UM
116
Figure 6-3. Operation Timing in Controller State
TCK
Controller state
Enters state
Starts in state
at falling edge of TCK pin
Starts in state
at rising edge of TCK pin
(1) Test-Logic-Reset
The boundary scan circuit performs no operation on the
µ
PD98431. Therefore, it does not affect the system
logic of the
µ
PD98431. This is because the bypass instruction is stored to the instruction register and executed
on initialization. The TAP controller enters the Test-Logic-Reset state if the TMS pin holds the high level for the
duration of at least five rising edges of the TCK pin signal, regardless of the current state of the controller. The
TAP controller holds this state for the duration in which the TMS pin signal high.
If the TAP controller must be in the Test-Logic-Reset state, the controller returns to the original Test-Logic-Reset
state even if a low-level signal is input once to the TMS pin by mistake (due to, for example, the influence of the
external interface), if the TMS pin signal holds its high level status for the duration of three rising edges of the
TCK pin signal.
The operation of the test logic does not hinder the logic operation of the
µ
PD98431 due to the above error.
When the TAP controller exits from the Test-Logic-Reset state, the controller enters the Run-Test/Idle state. In
this state, no operation is performed because the current instruction is set by the operation of the bypass
register. The logic operation of the JTAG boundary scan circuit is inactive even in the Select-DR-Scan and
Select-IR-Scan states.
(2) Run-Test/Idle
The TAP controller is in this state during scan operation (in Select-DR-Scan or Select-IR-Scan state). Once the
controller has entered this state and if the TMS pin signal holds the low level, the controller remains in this state.
The controller enters the Select-DR-Scan state if the TMS pin signal holds high level at one rising edge of the
TCK pin signal.
All the test data registers (boundary register and bypass register) selected by the current instruction hold the
previous status (Idle). While the TAP controller is in this state, the instruction does not change.
(3) Select-DR-Scan
This is a temporary boundary scan state. The boundary scan register and bypass register selected by the
current instruction hold the previous state.
If the TMS pin signal is held low at the rising edge of the TCK pin signal while the TAP controller is in this state,
the controller enters the Capture-DR state, and scan sequence to the selected registers is started.
If the TMS pin signal is held high at the rising edge of the TCK pin signal, the TAP controller enters the Select-IR-
Scan state. While the controller is in this state, the instruction does not change.
Содержание mPD98431
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