LM3S610 Data Sheet
October 8, 2006 47
Preliminary
5.4 Register Descriptions
There are no APB-accessible registers in the JTAG TAP Controller or Shift Register chains. The
registers within the JTAG controller are all accessed serially through the TAP Controller. The
registers can be broken down into two main categories: Instruction Registers and Data Registers.
5.4.1 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.
5.4.1.1 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.
5.4.1.2 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
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 Captu res the c urren t I/O val ue s an d sh if t s the sam pl ed v alu es 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.
