
Debug Support
8-16
Copyright 1999, 2000 ARM Limited. All rights reserved.
ARM DDI 0144B
When the BYPASS instruction is loaded into the instruction register, all the scan cells
are placed in their normal (System) mode of operation. This instruction has no effect on
the system pins.
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 using
TDI
and out
using
TDO
after a delay of one
TCK
cycle. The first bit shifted out is a zero.
The bypass register is not affected in the UPDATE-DR state.
Note
All unused instruction codes default to the BYPASS instruction.
CLAMP (0101)
This instruction connects a 1-bit shift register (the BYPASS register) between
TDI
and
TDO
.
When the CLAMP instruction is loaded into the instruction register, the state of all the
output signals is defined by the values previously loaded into the currently loaded scan
chain.
Note
This instruction must only be used when scan chain 0 is the currently selected scan
chain.
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 using
TDI
and out
using
TDO
after a delay of one
TCK
cycle. The first bit shifted out is a zero.
The bypass register is not affected in the UPDATE-DR state.
HIGHZ (0111)
This instruction connects a 1-bit shift register (the BYPASS register) between
TDI
and
TDO
.
When the HIGHZ instruction is loaded into the instruction register and scan chain 0 is
selected, all ARM9TDMI outputs are driven to the high-impedance state, and the
external
HIGHZ
signal is driven HIGH. This functions as if the ARM9TDMI signal
TBE
had been driven LOW.