Problème programmation Pin

What do you mean by perturbated ?

In your schema, the net_31 will not go higher than {3.3V + VLed}.

If CPLD was not connected,

your Led will emitting light if TS> {3.3V + VLed}

if TS < {3.3V + VLed}, no source drives the net_31.

The voltage level of net_31 would depend of Ts with R and design of the AOP (Operationnal Ampli), and it would be too sensitive.

To resume : if ts=0, net_31 is unknown.

Here, Led is functionning as a clamping Diode : is it exactly what you want ? (not sure)

Check carefully your CPLD pins option.

Try also / look at :

- unused input tri-stated pin option in Quartus (if you are using Quartus)

- inout pin

- open drain pin