
Signal Descriptions
ARM DDI 0192A
Copyright ARM Limited 1997, 1998, 2000. All rights reserved.
A-7
A.3
JTAG signals
JTAG signal descriptions are listed in Table A-3.
Table A-3 JTAG signal descriptions
Name
Type
Description
HIGHZ
Out
This signal denotes that the
HIGHZ
instruction has been loaded into the TAP controller.
IR[3:0]
Out
TAP instruction register.
These signals reflect the current instruction loaded into the TAP controller instruction register.
The signals change on the falling edge of
XTCK
when the TAP state machine is in the
UPDATE-DR state. You can use these signals to allow more scan chains to be added using the
ARM720T TAP controller.
RSTCLKBS
Out
Reset boundary scan clock.
This signal denotes that either the TAP controller state machine is in the RESET state or that
XnTRST
has been asserted. You can use this to reset boundary scan cells outside the
ARM720T.
SCREG[3:0]
Out
Scan chain register.
These signals reflect the ID number of the scan chain currently selected by the TAP controller.
These signals change on the falling edge of
XTCK
when the TAP state machine is in the
UPDATE-DR state.
SDINBS
Out
Boundary scan serial data in.
This signal is the serial data to be applied to an external scan chain.
SDOUTBS
In
Boundary scan serial data out.
This signal is the serial data from an external scan chain. It allows a single
XTDO
port to be
used. If an external scan chain is not connected, this input must be tied LOW.
TAPSM[3:0]
Out
Tap controller status.
These signals represent the current state of the TAP controller machine. These signals change
on the rising edge of
XTCK
and can be used to allow more scan chains to be added using the
ARM720T TAP controller.
TCK1
Out
Test clock one.
This clock represents the HIGH phase of
XTCK
.
TCK1
is HIGH when
XTCK
is HIGH. This
signal can be used to allow more scan chains to be added using the ARM720T TAP controller.
TCK2
Out
Test clock two.
This clock represents the LOW phase of
XTCK
.
TCK2
is HIGH when
XTCK
is LOW. You
can use this signal to allow more scan chains to be added using the ARM720T TAP controller.
TCK2
is the non-overlapping complement of
TCK1
.
XnTDOEN
Out
Not test data out output enable.
When LOW, this signal denotes that serial data is being driven out on the
XTDO
output.