STARTUP

User Interface to Global Clock, Reset, and 3-State Controls

The STARTUP primitive is used for Global Set/Reset, global 3-state control, and the user configuration clock. The Global Set/Reset (GSR) input, when High, sets or resets every flip-flop in the device, depending on the initialization state (S or R) of the flip-flop. Following configuration, the global 3-state control (GTS), when High, forces all the IOB outputs into high impedance mode, which isolates the device outputs from the circuit but leaves the inputs active.

Including the STARTUP symbol in a design is optional. You must include the symbol under the following conditions.

• If you intend to exert external control over global set/reset, you must connect the GSR pin to an IPAD and an IBUF, as shown here. (For the XC5200, connect the GR pin to an IPAD and an IBUF.)
  
  
  
  
• If you intend to exert external control over global tristate, you must connect the GTS pin to an IPAD and IBUF, as shown here.
  
  
  
  
• If you wish to synchronize startup to a user clock, you must connect the user clock signal to the CLK input, as shown here. Furthermore, “user clock” must be selected in the BitGen program.
  
  

You can use location constraints to specify the pin from which GSR or GTS (or both) is accessed.

The STARTUP outputs (Q2, Q3, Q1Q4, and DONEIN) display the progress/status of the start-up process following the configuration. Refer to The Programmable Logic Data Book for additional details.