The device chain U1, U2, ... Un is a serial chain where U1 is the first device TDI enters and Un is the last device. Un must deliver the TDO (labelled RD on the XChecker cable) signal back to the cable. TMS and TCK signals enter all devices in parallel.
Figure 3.2 Device Chain |  |
The chain description must contain all devices in the order that they appear in the JTAG programming chain.
Alternatively, you can use the Initialize Chain operation to automatically identify the devices in the system boundary-scan chain. You must then associate JEDEC files for XC9500 CPLD devices, BIT files for Xilinx FPGA devices, and BSDL files for all other devices by using the device properties dialog box.
