
Debug Support
ARM DDI 0144B
Copyright 1999, 2000 ARM Limited. All rights reserved.
8-15
During the SHIFT-DR state, the ID number of the desired scan path is shifted into the
scan path select register.
In the UPDATE-DR state, the scan register of the selected scan chain is connected
between
TDI
and
TDO
, and remains connected until a subsequent SCAN_N instruction
is issued. On reset, scan chain 3 is selected by default. The scan path select register is
five bits long in this implementation, although no finite length is specified.
INTEST (1100)
The selected scan chain is placed in test mode by the INTEST instruction. The INTEST
instruction connects the selected scan chain between
TDI
and
TDO
.
When the instruction register is loaded with the INTEST instruction, all the scan cells
are placed in their test mode of operation.
In the CAPTURE-DR state, the value of the data applied from the core logic to the
output scan cells, and the value of the data applied from the system logic to the input
scan cells is captured.
In the SHIFT-DR state, the previously captured test data is shifted out of the scan chain
through the
TDO
pin, while new test data is shifted in using the
TDI
pin.
IDCODE (1110)
The IDCODE instruction connects the device identification register (or ID register)
between
TDI
and
TDO
. The ID register is a 32-bit register that allows the manufacturer,
part number and version of a component to be determined through the TAP.
When the instruction register is loaded with the IDCODE instruction, all the scan cells
are placed in their normal (system) mode of operation.
In the CAPTURE-DR state, the device identification code is captured by the ID register.
In the SHIFT-DR state, the previously captured device identification code is shifted out
of the ID register using the
TDO
pin, while data is shifted in using the
TDI
pin into the
ID register.
In the UPDATE-DR state, the ID register is unaffected.
BYPASS (1111)
The BYPASS instruction connects a 1-bit shift register (the BYPASS register) between
TDI
and
TDO
.