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DS21354 & DS21554
78 of 117
JTAG FUNCTIONAL BLOCK DIAGRAM
Figure 17-1
17.2 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 17-2.
Test-Logic-Reset
Upon power up, the TAP Controller will be 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.
+V
Boundary Scan
Register
Identification
Register
Bypass
Register
Instruction
Register
JTDI
JTMS
JTCLK
JTRST
JTDO
+V
+V
Test Access Port
Controller
MUX
10K
10K
10K
Select
Output Enable