Spartan-3 FPGA Family: Pinout Descriptions
DS099 (v3.1) June 27, 2013
Product Specification
120
IDCODE Register
Spartan-3 FPGAs contain a 32-bit identification register called the IDCODE register, as defined in the IEEE 1149.1 JTAG
standard. The fixed value electrically identifies the manufacture (Xilinx) and the type of device being addressed over a JTAG
chain. This register allows the JTAG host to identify the device being tested or programmed via JTAG. See
Table 78.
Using JTAG Port After Configuration
The JTAG port is always active and available before, during, and after FPGA configuration. Add the BSCAN_SPARTAN3
primitive to the design to create user-defined JTAG instructions and JTAG chains to communicate with internal logic.
Furthermore, the contents of the User ID register within the JTAG port can be specified as a Bitstream Generation option.
By default, the 32-bit User ID register contains 0xFFFFFFFF.
Precautions When Using the JTAG Port in 3.3V Environments
The JTAG port is powered by the +2.5V VCCAUX power supply. When connecting to a 3.3V interface, the JTAG input pins
must be current-limited using a series resistor. Similarly, the TDO pin is a CMOS output powered from +2.5V. The TDO
See also
XAPP453: The 3.3V Configuration of Spartan-3 FPGAs for additional details.
The following interface precautions are recommended when connecting the JTAG port to a 3.3V interface.
Avoid actively driving the JTAG input signals High with 3.3V signal levels. If required in the application, use series
current-limiting resistors to keep the current below 10 mA per pin.
If possible, drive the FPGA JTAG inputs with drivers that can be placed in high-impedance (Hi-Z) after using the JTAG
port. Alternatively, drive the FPGA JTAG inputs with open-drain outputs, which only drive Low. In both cases, pull-up
resistors are required. The FPGA JTAG pins have pull-up resistors to VCCAUX before configuration and optional
X-Ref Target - Figure 43
Figure 43: JTAG Port
Table 78: Spartan-3 JTAG IDCODE Register Values (hexadecimal)
Part Number
IDCODE Register
XC3S50
0x0140C093
XC3S200
0x01414093
XC3S400
0x0141C093
XC3S1000
0x01428093
XC3S1500
0x01434093
XC3S2000
0x01440093
XC3S4000
0x01448093
XC3S5000
0x01450093
Data In
Data Out
Mode Select
Clock
TDI
TMS
TCK
TDO
JTAG Port
DS099_4_04_020811