Intel
®
81341 and 81342 I/O Processors
December 2007
Developer’s Manual
Order Number: 315037-002US
1007
Test Logic Unit and Testability—Intel
®
81341 and 81342
20.2.1
TAP Pin Description
The internal test logic is accessed through the TAP pins. The following sections describe
some of the rules and permissions of the IEEE 1149.1a Standard for the TAP pins.
20.2.1.1 Test Clock (TCK)
This is the clock input for the test logic defined by this standard, i.e. the TAP controller
and associated registers. The TLU is a fully static design, thus all registers retain their
states indefinitely when
TCK
is stopped at “0” or “1”.
20.2.1.2 Test Mode Select (TMS)
This pin is used to control the operation of the TAP controller. The signal received at
TMS
is decoded by the TAP controller to control test operations. The state of
TMS
is
sampled on the rising edge of
TCK
. Internally, there is a weak pull-up on this pin to
provide a logic high when not driven, per standard definition.
20.2.1.3 Test Data Input (TDI)
This pin is used to provide serial input data to the instruction and test data registers.
Data at
TDI
is sampled on the rising edge of
TCK
. Data shifted from
TDI
through a
register to
TDO
appears non-inverted at
TDO
after a number of rising and falling edges
of
TCK
determined by the length of the instruction or test data register selected.
Internally, there is a weak pull-up on this pin to provide a logic high when not driven,
per standard definition.
20.2.1.4 Test Data Output (TDO)
This is the serial data output pin. Changes in the state of
TDO
occur only following the
falling edge of
TCK
while performing a shift operation. This pin is only driven while
scanning (in SHDR or SHIR states) otherwise it is in inactive (high Z) state. The non-
shift inactive state is provided to support parallel connection of
TDO
outputs at the
board or module level.
20.2.1.5 Asynchronous Reset (TRST#)
The
TRST#
signal is used to asynchronously reset the TAP controller and boundary-
scan registers. The TAP controller is not initialized by any other system input, including
system reset. The TAP controller initializes asynchronously on the falling edge of
TRST#
to the Test-Logic_Reset (initial) state. The TAP controller is initialized at power-
up by cirrostrati built into the test logic. Upon reset, the TAP instruction register
initializes to the IDCODE instruction. Internally, there is a weak pull-up on this pin to
provide a logic high when not driven.