[longassname]

You actually had a schematic of a much better hardware interface earlier on. Using an opamp comparator you are removing hysteresis. You want to do the opposite. The better schematic you had posted showed a shmitt trigger. I think that was Kashima's. That design will adjust the input to trigger on the correct signaling level and maintain hysteresis. In actuality you shouldn't need either. It's not a bad ttl signal. The voltage levels are what they are on purpose. The best thing to do is use the correct generation line driver/buffer/gate to match the signal.