Debug and Test Interface
14-7
GMS30C7201 Data Sheet
state, test data is shifted into the bypass register via
TDI
and out via
TDO
after a delay
of one
TCK
cycle. Note that the first bit shifted out will be a zero. The bypass register
is not affected in the UPDATE-DR state.
HIGHZ (0111)
The HIGHZ instruction connects a 1 bit shift register (the BYPASS register) between
TDI
and
TDO
. When the HIGHZ instruction is loaded into the instruction register, all
outputs are placed in an inactive drive state. In the CAPTURE-DR state, a logic 0 is
captured by the bypass register. In the SHIFT-DR state, test data is shifted into the
bypass register via
TDI
and out via
TDO
after a delay of one
TCK
cycle. Note that the
first bit shifted out will be a zero. The bypass register is not affected in the UPDATE-DR
state.
CLAMPZ (1001)
The CLAMPZ instruction connects a 1 bit shift register (the BYPASS register) between
TDI
and
TDO
.When the CLAMPZ instruction is loaded into the instruction register, all
outputs are placed in an inactive drive state, but the data supplied to the disabled output
drivers is derived from the boundary-scan cells. The purpose of this instruction is to
ensure, during production testing, that each output driver can be disabled when its data
input is either a 0 or a 1.A guarding pattern (specified for this device at the end of this
section) should be pre-loaded into the boundary-scan register using the SAMPLE/
PRELOAD instruction prior to selecting the CLAMPZ instruction. In the CAPTURE-DR
state, a logic 0 is captured by the bypass register. In the SHIFT-DR state, test data is
shifted into the bypass register via
TDI
and out via
TDO
after a delay of one
TCK
cycle.
Note that the first bit shifted out will be a zero. The bypass register is not affected in the
UPDATE-DR state.
INTEST (1100)
The BS (boundary-scan) register is placed in test mode by the INTEST instruction. The
INTEST instruction connects the BS register between
TDI
and
TDO
. When the
instruction register is loaded with the INTEST instruction, all the boundary-scan cells
are placed in their test mode of operation. In the CAPTURE-DR state, the complement
of the data supplied to the core logic from input boundary-scan cells is captured, while
the true value of the data that is output from the core logic to output boundary- scan
cells is captured. Note that CAPTURE-DR captures the complemented value of the
input cells for testability reasons. In the SHIFT-DR state, the previously captured test
data is shifted out of the BS register via the
TDO
pin, whilst new test data is shifted in
via the
TDI
pin to the BS register parallel input latch. In the UPDATE-DR state, the new
test data is transferred into the BS register parallel output latch. Note that this data is
applied immediately to the system logic and system pins. The first INTEST vector
should be clocked into the boundary-scan register, using the SAMPLE/PRELOAD
instruction, prior to selecting INTEST to ensure that known data is applied to the
system logic. Single-step operation is possible using the INTEST instruction.
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 The
IDCODE returned will be that for the ARM720T core. When the instruction register is
loaded with the IDCODE instruction, all the boundary-scan cells are placed in their
normal (system) mode of operation. In the CAPTURE-DR state, the device
identification code (specified at the end of this section) is captured by the ID register.
In the SHIFT-DR state, the previously captured device identification code is shifted out
of the ID register via the
TDO
pin, whilst data is shifted in via the
TDI
pin into the ID
register. In the UPDATE-DR state, the ID register is unaffected.