TM4C123AE6PM Datasheet, PDF (194/1237 Pages) Texas Instruments – Tiva TM4C123AE6PM Microcontroller

JTAG Interface
Table 4-1. JTAG_SWD_SWO Signals (64LQFP) (continued)
Pin Name
Pin Number Pin Mux / Pin Pin Type Buffer Type^a Description
Assignment
TMS
51
PC1 (1)
I
TTL
JTAG TMS and SWDIO.
a. The TTL designation indicates the pin has TTL-compatible voltage levels.
4.3 Functional Description
A high-level conceptual drawing of the JTAG module is shown in Figure 4-1 on page 193. The JTAG
module is composed of the Test Access Port (TAP) controller and serial shift chains with parallel
update registers. The TAP controller is a simple state machine controlled by the TCK and TMS inputs.
The current state of the TAP controller depends on the sequence of values captured on TMS at the
rising edge of TCK. The TAP controller determines when the serial shift chains capture new data,
shift data from TDI towards TDO, and update the parallel load registers. The current state of the
TAP controller also determines whether the Instruction Register (IR) chain or one of the Data Register
(DR) chains is being accessed.
The serial shift chains with parallel load registers are comprised of a single Instruction Register (IR)
chain and multiple Data Register (DR) chains. The current instruction loaded in the parallel load
register determines which DR chain is captured, shifted, or updated during the sequencing of the
TAP controller.
Some instructions, like EXTEST, operate on data currently in a DR chain and do not capture, shift,
or update any of the chains. Instructions that are not implemented decode to the BYPASS instruction
to ensure that the serial path between TDI and TDO is always connected (see Table 4-3 on page 200
for a list of implemented instructions).
See “JTAG and Boundary Scan” on page 1194 for JTAG timing diagrams.
Note:
Of all the possible reset sources, only Power-On reset (POR) and the assertion of the RST
input have any effect on the JTAG module. The pin configurations are reset by both the
RST input and POR, whereas the internal JTAG logic is only reset with POR. See “Reset
Sources” on page 205 for more information on reset.
4.3.1
JTAG Interface Pins
The JTAG interface consists of four standard pins: TCK, TMS, TDI, and TDO. These pins and their
associated state after a power-on reset or reset caused by the RST input are given in Table 4-2.
Detailed information on each pin follows.
Note: The following pins are configured as JTAG port pins out of reset. Refer to “General-Purpose
Input/Outputs (GPIOs)” on page 594 for information on how to reprogram the configuration
of these pins.
Table 4-2. JTAG Port Pins State after Power-On Reset or RST assertion
Pin Name
TCK
TMS
TDI
TDO
Data Direction
Input
Input
Input
Output
Internal Pull-Up Internal Pull-Down
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
Disabled
Drive Strength
N/A
N/A
N/A
2-mA driver
Drive Value
N/A
N/A
N/A
High-Z
194
June 12, 2014
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