What must be done to interface TTL to CMOS?

• A dropping resistor must be used on the CMOS 12 V supply to reduce it to 5 V for the TTL.
• As long as the CMOS supply voltage is 5 V, they can be interfaced; however, the fan-out of the TTL is limited to five CMOS gates.
• A 5 V Zener diode must be placed across the inputs of the TTL gates in order to protect them from the higher output voltages of the CMOS gates.
• A pull-up resistor must be used between the TTL output-CMOS input node and Vcc; the value of RP will depend on the number of CMOS gates connected to the node.