
LM3S101 Data Sheet
March 22, 2006
40
Preliminary
5.3.1
Instruction Register (IR)
The JTAG TAP Instruction Register (IR) is a four-bit serial scan chain with a parallel load register
connected between the JTAG
TDI
and
TDO
pins. When the TAP Controller is placed in the correct
states, bits can be shifted into the Instruction Register. Once these bits have been shifted into the
chain and updated, they are interpreted as the current instruction. The decode of the Instruction
Register bits is shown in Table 5-2. A detailed explanation of each instruction, along with its
associated Data Register, follows.
5.3.1.1
EXTEST Instruction
The EXTEST instruction does not have an associated data register chain. The EXTEST instruction
uses the data that has been preloaded into the Boundary Scan data register using the SAMPLE/
PRELOAD instruction. When the EXTEST instruction is present in the Instruction Register, the
preloaded data in the Boundary Scan data register associated with the outputs and output enables
are used to drive the GPIO pads rather than the signals coming from the core. This allows tests to
be developed that drive known values out of the controller, which can be used to verify
connectivity.
5.3.1.2
INTEST Instruction
The INTEST instruction does not have an associated data register chain. The INTEST instruction
uses the data that has been preloaded into the Boundary Scan data register using the SAMPLE/
PRELOAD instruction. When the INTEST instruction is present in the Instruction Register, the
preloaded data in the Boundary Scan data register associated with the inputs are used to drive the
signals going into the core rather than the signals coming from the GPIO pads. This allows tests to
be developed that drive known values into the controller, which can be used for testing. It is
important to note that although the
RST
input pin is on the Boundary Scan data register chain, it is
only observable.
Table 5-2.
JTAG Instruction Register Commands
IR[3:0]
Instruction
Description
0000
EXTEST
Drives the values preloaded into the Boundary Scan Chain by the
SAMPLE/PRELOAD instruction onto the pads.
0001
INTEST
Drives the values preloaded into the Boundary Scan Chain by the
SAMPLE/PRELOAD instruction into the controller.
0010
SAMPLE / PRELOAD
Captures the current I/O values and shifts the sampled values out of the
Boundary Scan Chain while new preload data is shifted in.
1000
ABORT
Shifts data into the ARM Debug Port Abort register.
1010
DPACC
Shifts data into and out of the ARM DP Access register.
1011
APACC
Shifts data into and out of the ARM AC Access register.
1110
IDCODE
Loads manufacturing information defined by the
IEEE Standard 1149.1
into the IDCODE chain and shifts it out.
1111
BYPASS
Connects
TDI
to
TDO
through a single shift register chain.
All Others
Reserved
Defaults to the BYPASS instruction to ensure that
TDI
is always
connected to
TDO
.