LM3S5P3B Datasheet, PDF (179/1170 Pages) Texas Instruments – Stellaris® LM3S5P3B Microcontroller

Stellaris^® LM3S5P3B Microcontroller
4.3.2
chain being accessed. In order to save power when the JTAG port is not being used, the TDO pin
is placed in an inactive drive state when not actively shifting out data. Because TDO can be connected
to the TDI of another controller in a daisy-chain configuration, the IEEE Standard 1149.1 expects
the value on TDO to change on the falling edge of TCK.
By default, the internal pull-up resistor on the TDO pin is enabled after reset, assuring that the pin
remains at a constant logic level when the JTAG port is not being used. The internal pull-up and
pull-down resistors can be turned off to save internal power if a High-Z output value is acceptable
during certain TAP controller states (see page 443 and page 445).
JTAG TAP Controller
The JTAG TAP controller state machine is shown in Figure 4-2. The TAP controller state machine
is reset to the Test-Logic-Reset state on the assertion of a Power-On-Reset (POR). In order to reset
the JTAG module after the microcontroller has been powered on, the TMS input must be held HIGH
for five TCK clock cycles, resetting the TAP controller and all associated JTAG chains. Asserting
the correct sequence on the TMS pin allows the JTAG module to shift in new instructions, shift in
data, or idle during extended testing sequences. For detailed information on the function of the TAP
controller and the operations that occur in each state, please refer to IEEE Standard 1149.1.
Figure 4-2. Test Access Port State Machine
Test Logic Reset
1
0
Run Test Idle
1
0
Select DR Scan
1
0
Capture DR
1
0
Shift DR
1
0
Exit 1 DR
1
0
Pause DR
1
0
Exit 2 DR
0
1
Update DR
10
Select IR Scan
1
0
Capture IR
1
0
Shift IR
1
0
Exit 1 IR
1
0
Pause IR
1
0
Exit 2 IR
0
1
Update IR
10
4.3.3
Shift Registers
The Shift Registers consist of a serial shift register chain and a parallel load register. The serial shift
register chain samples specific information during the TAP controller’s CAPTURE states and allows
January 20, 2012
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