0
0
TDO
TDI
Version
Part Number
Manufacturer ID
31 28 27
12 11
1 0
TDO
TDI
1
Register Descriptions
192
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
JTAG Interface
3.5.1.7
BYPASS Instruction
The BYPASS instruction connects the associated BYPASS Data Register chain between TDI and TDO.
This instruction is used to create a minimum length serial path between the TDI and TDO ports. The
BYPASS Data Register is a single-bit shift register. This instruction improves test efficiency by allowing
components that are not needed for a specific test to be bypassed in the JTAG scan chain by loading
them with the BYPASS instruction. See
for more information.
3.5.2 Data Registers
The JTAG module contains six Data Registers. These serial Data Register chains include: IDCODE,
BYPASS, Boundary Scan, APACC, DPACC, and ABORT and are discussed in the following sections.
3.5.2.1
IDCODE Data Register
shows the format for the 32-bit IDCODE Data Register defined by the IEEE Standard 1149.1.
The standard requires that every JTAG-compliant microcontroller implement either the IDCODE instruction
or the BYPASS instruction as the default instruction. The LSB of the IDCODE Data Register is defined to
be a 1 to distinguish it from the BYPASS instruction, which has an LSB of 0. This definition allows auto-
configuration test tools to determine which instruction is the default instruction.
The major uses of the JTAG port are for manufacturer testing of component assembly and program
development and debug. To facilitate the use of auto-configuration debug tools, the IDCODE instruction
outputs a value of 0x4BA0.0477. This value allows the debuggers to automatically configure themselves to
work correctly with the Cortex-M4F during debug.
Figure 3-3. IDCODE Register Format
3.5.2.2
BYPASS Data Register
shows the format for the 1-bit BYPASS Data Register defined by the IEEE Standard 1149.1.
The standard requires that every JTAG-compliant microcontroller implement either the BYPASS
instruction or the IDCODE instruction as the default instruction. The LSB of the BYPASS Data Register is
defined to be a 0 to distinguish it from the IDCODE instruction, which has an LSB of 1. This definition
allows auto-configuration test tools to determine which instruction is the default instruction.
Figure 3-4. BYPASS Register Format
3.5.2.3
Boundary Scan Data Register
The format of the Boundary Scan Data Register is shown in
. Each GPIO pin, starting with a
GPIO pin next to the JTAG port pins, is included in the Boundary Scan Data Register. Each GPIO pin has
three associated digital signals that are included in the chain. These signals are input, output, and output
enable, and are arranged in that order as shown in the figure.
When the Boundary Scan Data Register is accessed with the SAMPLE/PRELOAD instruction, the input,
output, and output enable from each digital pad are sampled and then shifted out of the chain to be
verified. The sampling of these values occurs on the rising edge of TCK in the Capture DR state of the
TAP controller. While the sampled data is being shifted out of the Boundary Scan chain in the Shift DR
state of the TAP controller, new data can be preloaded into the chain for use with the EXTEST instruction.
The EXTEST instruction forces data out of the controller.