Dumb question. Can't seem to understand how pull up resistor works when interfacing TTL to CMOS. A TTL output connected to a CMOS input. TTL output is 3.3V, but CMOS requires 5V. When TTL output is high, one end of resistor is 3.3V and the other end is 5V. The 3.3V end is connected to cmos input. How does the cmos input see 5V? ckt diagram here -http://www.ecelab.com/interfacing-ttl-cmos.htm Also, how do you decide the value of the resistor?