What is the difference between "concurrent" and "sequential" programming modes?
iMPACT normally programs devices sequentially; it selects a device to program and sets all other devices in the boundary-scan chain to BYPASS mode.
Some devices (such as the XC9500, CoolRunner CPLDs, and 18V00 ISP PROMs) require iMPACT to wait at certain times during the programming process. With concurrent programming, if multiple CPLD or PROM devices exist in the JTAG chain, iMPACT can use this wait time to program a portion of another device. This can reduce the amount of time required to program a chain of CPLD or PROM devices.
To enable toggling between concurrent/sequential mode, go to Edit -> Preferences and uncheck the "Concurrent Mode" box.