AR# 151: XC2000/XC3000/XC4000/XC5200: What set, reset capabilities do the 2000. 4000, 5200 flip flops have?
AR# 151
XC2000/XC3000/XC4000/XC5200: What set, reset capabilities do the 2000. 4000, 5200 flip flops have?
描述
Keywords
解决方案
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.