Pin Descriptions
v1.1
10- 5
Note that to operate at all VJTAG voltages, 500 Ω to 1 kΩ will satisfy the requirements. Refer to
TDI
Test Data Input
Serial input for JTAG boundary scan, ISP, and UJTAG usage. There is an internal weak pull-up
resistor on the TDI pin.
TDO
Test Data Output
Serial output for JTAG boundary scan, ISP, and UJTAG usage.
TMS
Test Mode Select
The TMS pin controls the use of the IEEE 1532 boundary scan pins (TCK, TDI, TDO, TRST). There is an
internal weak pull-up resistor on the TMS pin.
TRST
Boundary Scan Reset Pin
The TRST pin functions as an active-low input to asynchronously initialize (or reset) the boundary
scan circuitry. There is an internal weak pull-up resistor on the TRST pin. If JTAG is not used, an
external pull-down resistor could be included to ensure the test access port (TAP) is held in reset
mode. The resistor values must be chosen from
Table 10-2 and must satisfy the parallel resistance
value requirement. The values in
Table 10-2 correspond to the resistor recommended when a single
device is used, and the equivalent parallel resistor when multiple devices are connected via a JTAG
chain.
In critical applications, an upset in the JTAG circuit could allow entrance to an undesired JTAG
state. In such cases, Actel recommends tying off TRST to GND through a resistor placed close to the
FPGA pin.
Note that to operate at all VJTAG voltages, 500 Ω to 1 kΩ will satisfy the requirements.
Special Function Pins
NC
No Connect
This pin is not connected to circuitry within the device. These pins can be driven to any voltage or
can be left floating with no effect on the operation of the device.
DC
Do Not Connect
This pin should not be connected to any signals on the PCB. These pins should be left unconnected.
Table 10-2 Recommended Tie-Off Values for the TCK and TRST Pins
VJTAG
Tie-Off Resistance
VJTAG at 3.3 V
200
Ω to 1 kΩ
VJTAG at 2.5 V
200
Ω to 1 kΩ
VJTAG at 1.8 V
500
Ω to 1 kΩ
VJTAG at 1.5 V
500
Ω to 1 kΩ
Notes:
1. Equivalent parallel resistance if more than one device is on the JTAG chain
2. The TCK pin can be pulled up/down.
3. The TRST pin is pulled down.