Answers Database

XC2000/XC3000/XC4000/XC5200: What set, reset capabilities do the 2000. 4000, 5200 flip flops have?


Record #151

Problem Title:
XC2000/XC3000/XC4000/XC5200: What set, reset capabilities do the 2000.
4000, 5200 flip flops have?



Problem Description:
Keywords


Solution 1:




Due to architectural differences in the flip flops in the 2, 3, and 4k families
of devices, the same set and reset abilities are not available to them all;

2000:  FFs can both set and reset asynchronously.

3000:  FFs can only reset asynchronously.

4000E/EX/XL/XV:  FFs can either set OR reset asychronously, but not both.




3000: Latches are not reliable because of potential timing
issues. User should be aware min timing specs are not
specified.

4000e: Latches maybe safely implemented using RAM. Look at
solution 122 for more details. However, the ones present in
the library may have the same problems as the XC3000.

4000ex/xl/xv: The CLBs in these devices contain latches and
can be safely used.



End of Record #151