Pin Descriptions
3-4 Revision 17
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 Tab le 3-2 and must satisfy the parallel resistance value
requirement. The values in Ta ble 3 -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, Microsemi recommends tying off TRST to GND through a resistor placed close to the FPGA
pin.
Note that to operate at all VJTAG voltages, 500 to 1 k 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.
Packaging
Semiconductor technology is constantly shrinking in size while growing in capability and functional
integration. To enable next-generation silicon technologies, semiconductor packages have also evolved
to provide improved performance and flexibility.
Microsemi consistently delivers packages that provide the necessary mechanical and environmental
protection to ensure consistent reliability and performance. Microsemi IC packaging technology
efficiently supports high-density FPGAs with large-pin-count Ball Grid Arrays (BGAs), but is also flexible
enough to accommodate stringent form factor requirements for Chip Scale Packaging (CSP). In addition,
Microsemi offers a variety of packages designed to meet your most demanding application and economic
requirements for today's embedded and mobile systems.
Table 3-3 • TRST and TCK Pull-Down Recommendations
VJTAG Tie-Off Resistance*
VJTAG at 3.3 V 200 to 1 k
VJTAG at 2.5 V 200 to 1 k
VJTAG at 1.8 V 500 to 1 k
VJTAG at 1.5 V 500 to 1 k
Note: Equivalent parallel resistance if more than one device is on the JTAG chain
