Here’s a brief, practical overview of the popular logic gates from the Polish UCY74xx series. I’ve focused here on providing a practical illustration of how each circuit works. Below you’ll find a discussion of the classic chips that implement NAND, NOR, NOT and AND functions. I have described each gate using the relevant Boolean equation and truth table, and I have combined theory with practice using video recordings in which I demonstrate how these circuits respond to logic states triggered by buttons.
The original 7400 series, introduced into mass production by Texas Instruments, was one of the first digital integrated circuits manufactured using TTL technology. Over the years, these circuits have seen many versions, such as the high-speed (74S) and low-current (74LS) variants, as well as CMOS versions (the HC and HCT series). The specific letter designations depended on the version and manufacturer – for example, in Poland these chips were manufactured by CEMI under the name UCY. During the heyday of TTL technology, and thus at the turn of the 1970s and 1980s, this was the fundamental building block of digital electronic circuits.
UCY series circuits are available in versions with different output stage configurations. Alongside standard outputs, the list below also includes open-collector versions (allowing, amongst other things, the control of higher-voltage loads) and buffered versions (with increased current capacity, used to drive more demanding components).
The UCY7401 comprises four two-input open-collector NAND gates. These implement the negated logical product (NAND) function.
The function can be expressed by the formula:
$$Y = \overline{A \cdot B}$$
The truth table shows that the function returns a high level only when at least one of the inputs is at a low level:
| A | B | Y |
| 1 | 1 | 0 |
| 0 | X | 1 |
| X | 0 | 1 |
UCY7401 pinout:
Video demonstration – the LED is connected between the output and the power supply, so when it lights up, this indicates a low state. For the sake of simplicity, I’ve connected the inputs to earth, even though with TTL this requires slightly lower resistor values and draws more current; however, I wanted pressing a button to indicate a high state. The video shows that the LED lights up only when both buttons are pressed.
UCY7402 these are four two-input NOR gates. They implement the negated logical OR (NOR).
The function can be expressed by the formula:
$$Y = \overline{A + B}$$
The truth table shows that the function returns a high state only when all inputs are in a low state:
| A | B | Y |
| 1 | X | 0 |
| X | 1 | 0 |
| 0 | 0 | 1 |
UCY7402 pinout:
Video demonstration – unlike the previous video, now you just need to press a single button to light up the LED:
UCY7404 consists of six NOT inverters. They perform the logical NOT function.
The function can be expressed by the formula:
$$Y = \overline{A}$$
The truth table shows that the function returns a high state only when the input is low:
| A | Y |
| 0 | 1 |
| 1 | 0 |
UCY7404 pin-out:
The 7404 video presentation hardly needs any commentary:
UCY7406 is also a six-channel NOT inverter, but in this case with open-collector outputs.
This also allows for the control of loads powered by higher voltages (in the case of the 7406, up to 30V, which facilitates, for example, the control of relays) and for the direct connection of multiple outputs to one another on a single signal line.
UCY7407 These are six non-inverting open-collector buffers. They act as logic buffers.
The function can be expressed by the formula:
$$Y = A$$
The truth table shows that the function returns a high level only when the input is high:
| A | Y |
| 0 | 0 |
| 1 | 1 |
UCY7407 pinout:
UCY7408 these are four two-input AND gates. They implement the logical product (AND).
The function can be expressed by the formula:
$$Y = A \cdot B$$
The truth table shows that the function returns a high level only when all inputs are high:
| A | B | Y |
| 1 | 1 | 1 |
| 0 | X | 0 |
| X | 0 | 0 |
UCY7408 pinout:
As the operation of this circuit is self-explanatory, I shall omit the presentation.
UCY7410 is a circuit comprising three three-input NAND gates. These implement the logical NOT-AND (NAND) function.
The function can be expressed by the formula:
$$Y = \overline{A \cdot B \cdot C}$$
The truth table shows that the function returns a high state only when at least one of the inputs is in a low state:
| A | B | C | Y |
| 1 | 1 | 1 | 0 |
| 0 | X | X | 1 |
| X | 0 | X | 1 |
| X | X | 0 | 1 |
Derivations:
Video presentation:
UCY7420 are two four-input NAND gates. They implement the negated logical AND (NAND) function.
The function can be expressed by the formula:
$$Y = \overline{A \cdot B \cdot C \cdot D}$$
The truth table shows that the function returns a high state only when at least one of the inputs is in a low state:
| A | B | C | D | Y |
| 1 | 1 | 1 | 1 | 0 |
| 0 | X | X | X | 1 |
| X | 0 | X | X | 1 |
| X | X | 0 | X | 1 |
| X | X | X | 0 | 1 |
Video presentation:
This circuit is also available in a buffered version – UCY7440 – with increased output current capacity, allowing it to drive a heavier load.
UCY7430 is a circuit comprising a single eight-input NAND gate. It performs the logical NOT AND (NAND) function for as many as eight variables.
The function can be expressed by the formula:
$$Y = \overline{A \cdot B \cdot C \cdot D \cdot E \cdot F \cdot G \cdot H}$$
The truth table shows that the function returns a high state only when at least one of the eight inputs is in a low state:
| A | B | C | D | E | F | G | H | Y |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 |
| 0 | X | X | X | X | X | X | X | 1 |
| X | 0 | X | X | X | X | X | X | 1 |
| X | X | 0 | X | X | X | X | X | 1 |
| X | X | X | 0 | X | X | X | X | 1 |
| X | X | X | X | 0 | X | X | X | 1 |
| X | X | X | X | X | 0 | X | X | 1 |
| X | X | X | X | X | X | 0 | X | 1 |
| X | X | X | X | X | X | X | 0 | 1 |
UCY7430 pinout:
I’ve skipped the video this time; it’s essentially the same as before – you can just picture eight buttons.
UCY7450 is a chip containing two two-input AND-OR-INVERT (AND-NOR), one of which is expandable. They implement a complex logical function.
The function can be expressed by the formula:
$$Y = \overline{(A \cdot B) + (C \cdot D)}$$
The truth table shows that the function returns a low state only when both inputs of the first or second product are in a high state:
| A | B | C | D | Y |
| 1 | 1 | X | X | 0 |
| X | X | 1 | 1 | 0 |
| 0 | X | 0 | X | 1 |
| 0 | X | X | 0 | 1 |
| X | 0 | 0 | X | 1 |
| X | 0 | X | 0 | 1 |
UCY7450 pinout:
This is clearly shown in the video demonstration – I have to press either the first pair of buttons or the second pair of buttons for the LED to light up:
The UCY7451 is a chip containing two two-input AND-OR-INVERT (AND-NOR) gates. It performs the same logical function as the 7450 model, but does not have pins for an expander (this chip is not expandable).
UCY7451 pins:
Video presentation:
That’s enough for now. Of course, these weren’t all the circuits in this series, as the range produced by CEMI was very extensive. I’ve actually left quite a lot out, as I’ve focused here exclusively on the simplest logic gates – I intend to cover more complex sequential and combinational circuits in a separate post. Take the UCY7475, for example – it’s already waiting in my drawer to be connected.
What else is in store for a presentation? Too many to list and write down – a wide variety of circuits, but including, amongst others, the UCY7475, UCY7472, UCY74150, UCY75107, UCY74164, 7U4154PC, MC146818P, MH74141, MH7490A, UCA6473 and ULY7710.
To sum up, the old UCY series chips, despite the passage of several decades, are still fully functional and fascinating components. Their simple, purely hardware-based nature makes them excellent material for learning the basics of digital technology. I’d encourage everyone to dig these classics out of a drawer and have a go experimenting with them on a breadboard.
Have you come across circuits like these, and if so, when, in which devices, and how would you rate their reliability?
Cool? Ranking DIY Helpful post? Buy me a coffee.
. I sometimes go back to them and build retro circuits, such as RAM using the UCY7489 (it’s interesting that a single chip like this draws up to 100mA). As for the practicality of using such chips today, apart from for educational purposes or out of nostalgia, there isn’t much point. 
