LM3S3768 Luminary Micro, Inc, LM3S3768 Datasheet - Page 57

• Manufacturer Part Number: LM3S3768
• Description: Lm3s3768 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

5.2.1.4
5.2.2
June 02, 2008
Test Data Output (TDO)
The TDO pin provides an output stream of serial information from the IR chain or the DR chains.
The value of TDO depends on the current TAP state, the current instruction, and the data in the
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. This assures 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.
JTAG TAP Controller
The JTAG TAP controller state machine is shown in Figure 5-2 on page 58. The TAP controller
state machine is reset to the Test-Logic-Reset state on the assertion of a Power-On-Reset (POR).
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.
Preliminary
LM3S3768 Microcontroller
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