
JTAG Interface
41
March 22, 2006
Preliminary
5.3.1.3
SAMPLE/PRELOAD Instruction
The SAMPLE/PRELOAD instruction connects the Boundary Scan data register chain between 
TDI
 and 
TDO
. This instruction samples the current state of the pad pins for observation and 
preloads new test data. Each GPIO pad has an associated input, output, and output enable signal. 
When the TAP controller enters the Capture DR state during this instruction, the input, output, and 
output-enable signals to each of the GPIO pads is captured. These samples are serially shifted out 
of 
TDO
 while the TAP controller is in the Shift DR state and can be used for observation or 
comparison in various tests.
While these samples of the inputs, outputs, and output enables are being shifted out of the 
Boundary Scan data register, new data is being shifted into the Boundary Scan data register from 
TDI
. Once the new data has been shifted into the Boundary Scan data register, the data is saved 
in the parallel load registers when the TAP controller enters the Update DR state. This update of 
the parallel load register preloads data into the Boundary Scan data register that is associated with 
each input, output, and output enable. This preloaded data can be used with the EXTEST and 
INTEST instructions to drive data into or out of the controller. Please see “Boundary Scan Data 
Register” on page 42 for more information.
5.3.1.4
ABORT Instruction
The ABORT instruction connects the associated ABORT data register chain between 
TDI
 and 
TDO
. This instruction provides read and write access to the ABORT register of the ARM Debug 
Access Port (DAP). Shifting the proper data into this data register clears various error bits or 
initiates a DAP abort of a previous request. Please see the “ABORT Data Register” on page 43 for 
more information.
5.3.1.5
DPACC Instruction
The DPACC instruction connects the associated DPACC data register chain between 
TDI
 and 
TDO
. This instruction provides read and write access to the DPACC register of the ARM Debug 
Access Port (DAP). Shifting the proper data into this register and reading the data output from this 
register allows read and write access to the ARM debug and status registers. Please see “DPACC 
Data Register” on page 43 for more information.
5.3.1.6
APACC Instruction
The APACC instruction connects the associated APACC data register chain between 
TDI
 and 
TDO
. This instruction provides read and write access to the APACC register of the ARM Debug 
Access Port (DAP). Shifting the proper data into this register and reading the data output from this 
register allows read and write access to internal components and buses through the Debug Port. 
Please see “APACC Data Register” on page 43 for more information.
5.3.1.7
IDCODE Instruction
The IDCODE instruction connects the associated IDCODE data register chain between 
TDI
 and 
TDO
. This instruction provides information on the manufacturer, part number, and version of the 
controller. This information can be used by testing equipment and debuggers to automatically 
configure their input and output data streams. IDCODE is the default instruction that is loaded into 
the JTAG Instruction Register when a power-on-reset (POR) is asserted, 
TRST
 is asserted, or the 
Test-Logic-Reset state is entered. Please see “IDCODE Data Register” on page 42 for more 
information.
5.3.1.8
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