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TTL to CMOS interfacing

This page covers TTL to CMOS IC interfacing and CMOS to TTL IC interfacing. It also mentions how to interface LED and Lamps with TTL or CMOS IC.

Figure-1 depicts TTL to CMOS interfacing and CMOS to TTL interfacing circuits. When 5V supply is given to TTL and CMOS ICs, logic levels of TTL and CMOS are different. One TTL IC can drive any number of CMOS ICs. However, TTL output in 'high state' yields 2.4 Volt which is lower than the minimum voltage required by CMOS IC (which is 3.5V) . For TTL to CMOS interfacing, standard pull up resistor is connected which solves the interfacing problem as mentioned. This is shown in figure-1(a).

CMOS to TTL interfacing

TTL and CMOS interfacing

A CMOS IC can easily drive any low power schottky TTL IC directly. But to interface standard TTL IC, buffer is provided in between CMOS and TTL ICs. This is shown in figure-1(b).

How to interface TTL and CMOS to LEDs and Lamps?

TTL CMOS interfacing with LED

Figure-2 depicts interfacing TTL or CMOS IC with LED. As shown in figure-2(a), high state output from TTL or CMOS will light the LED ON. The other configuration in which Low state will drive the LED to ON state in shown in figure-2(b).

TTL CMOS interfacing Lamp

Figure-3 depicts interfacing TTL or CMOS IC with Lamp. As lamp requires higher current, they are interfaced using transistors. Darlington pair is used to amplify the current even further as required which is shown in figure-3(b). In both of these cases, lamp will become ON when output of TTL or CMOS IC is in 'high' logic state.


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