eX Automotive Family FPGAs
Boundary Scan Testing (BST)
All eX devices are IEEE 1149.1 compliant. eX devices offer
superior diagnostic and testing capabilities by providing
Boundary Scan Testing (BST) and probing capabilities.
These functions are controlled through the special test
pins (TMS, TDI, TCK, TDO and TRST). The functionality of
each pin is defined by two available modes, Dedicated
and Flexible, and is described in
In the
dedicated test mode, TCK, TDI, and TDO are dedicated
pins and cannot be used as regular I/Os. In flexible mode
(default mode), TMS should be set High through a pull-
up resistor of 10 kΩ. TMS can be pulled Low to initiate
the test sequence.
Table 1-3 •
Boundary Scan Pin Functionality
Dedicated Test Mode
Flexible Mode
Flexible Mode
In Flexible mode, TDI, TCK and TDO may be used as
either user I/Os or as JTAG input pins. The internal
resistors on the TMS and TDI pins are disabled in flexible
JTAG mode, and an external 10 kΩ pull-resistor to V
CCI
is
required on the TMS pin.
To select the Flexible mode, users need to uncheck the
"Reserve JTAG" box in "Device Selection Wizard" in
Actel Designer software. The functionality of TDI, TCK,
and TDO pins is controlled by the BST TAP controller. The
TAP controller receives two control inputs; TMS and TCK.
Upon power-up, the TAP controller enters the Test-Logic-
Reset state. In this state, TDI, TCK, and TDO function as
user I/Os. The TDI, TCK, and TDO pins are transformed
from user I/Os into BST pins when the TMS pin is Low at
the first rising edge of TCK. The TDI, TCK, and TDO pins
return to user I/Os when TMS is held High for at least five
TCK cycles.
describes
the
different
configuration
requirements of BST pins and their functionality in
different modes.
Table 1-4 •
Boundary Scan Pin Configurations and
Functions
Designer
"Reserve JTAG"
Selection
Checked
Unchecked
Unchecked
TAP Controller
State
Any
Test-Logic-Reset
Any EXCEPT Test-
Logic-Reset
TCK, TDI, TDO are dedicated TCK, TDI, TDO are flexible and
BST pins
may be used as I/Os
No need for pull-up resistor for Use a pull-up resistor of 10 k
Ω
TMS and TDI
on TMS
Dedicated Test Mode
In Dedicated mode, all JTAG pins are reserved for BST;
designers cannot use them as regular I/Os. An internal
pull-up resistor is automatically enabled on both TMS
and TDI pins, and the TMS pin will function as defined in
the IEEE 1149.1 (JTAG) specification.
To select Dedicated mode, users need to reserve the JTAG
pins in Actel's Designer software by checking the
"Reserve JTAG" box in "Device Selection Wizard"
JTAG pins comply with LVTTL/TTL I/O
specification regardless of whether they are used as a
user I/O or a JTAG I/O. Refer to the
for detailed
specifications.
Mode
Dedicated (JTAG)
Flexible (User I/O)
Flexible (JTAG)
TRST Pin
The TRST pin functions as a dedicated Boundary-Scan
Reset pin when the "Reserve JTAG Test Reset" option is
selected as shown in
An internal pull-up
resistor is permanently enabled on the TRST pin in this
mode. It is recommended to connect this pin to GND in
normal operation to keep the JTAG state controller in
the Test-Logic-Reset state. When JTAG is being used, it
can be left floating or be driven High.
When the "Reserve JTAG Test Reset" option is not
selected, this pin will function as a regular I/O. If unused
as an I/O in the design, it will be configured as a tristated
output.
Figure 1-12 •
Device Selection Wizard
1 -8
v3.2
ACTEL [ Actel Corporation ]
