AR# 8245: 2.1i : 9500 : Hprep6 : Inverted global tristates do not tristate properly
2.1i : 9500 : Hprep6 : Inverted global tristates do not tristate properly
Keywords: 2.1i, hprep6, CPLD, 9500, tristate, global
General Description: I am using an inverted global tristate in my design, and although the simulation is fine, it does not work in the hardware. The tristate signal is never released, even though the control signal states it should be.
A problem has been found in the CPLD fitter and how it handles inverted tristate controls. The conditions that cause this to occur are:
- Must be using 9536/9572/95108 (XL not affected, the other 9500 devices not affected)
- Must use the positive AND negative form of the global tristate for the entire design. If the global tristates are ALL in the positive form OR all in the negative form, there is no problem.
The workaround is to UNCHECK under the Design Manager Options: Use Global Output Enable(s)