In general, is 5V CMOS compatible with 5V TTL?
No, in general you can not interface generic &quot;5V CMOS&quot; with generic &quot;5V TTL&quot;.
For any given two devices you must, as a minimum, make sure that the worst-case output voltages of the driver satisfy the worst-case input voltage requirements of the receiver. In other words, compare \$V_{OH}\$ to \$V_{IH}\$ and compare \$V_{OL}\$ to \$V_{IL}\$. Just in case this is an exam/homework question I'll leave a few details up to you.