Not really following,
the 4026 is basically a bunch of logic gates?
So the 4026 is made of a number of 7400 chips?
and when a certain voltage is meant it goes high meaning numbers increment by one as each output goes high due to a high voltage?
Hy John,
Firstly, I made another major mistake and assumed that the CD4026 is part of the 74xxx series family of logic chips, but it's not. It is part of the CD4xxx Complimentary Metal Oxide Silicon [Semiconductor] (CMOS) family. In the CD4xxx family, a hex NOR gate is the, CD4009, a quad TWO INPUT AND gate, CD4011, and a quad TWO INPUT NOR gate, CD4002.
But the mistake makes no difference to the principle of the explanation. The 74xxx and CD4xxx are the two major logic families in electronics, but the former now predominates, so much so, that the original TTL logic functions and pin outs are now made in CMOS too. CMOS is now the most widely deployed technology in digital integrated circuits: memory, microprocessors etc, but that CMOS is fantastically advanced and is based on unbelievably small geometries, resulting in lightning fast speeds and relatively low power consumption.
Basically TTL is fast but consumes a considerable amount of current from the 5V supply rail. On the other hand, CMOS is relatively slow (in electronic terms) and consumes virtually no current from the 5V supply rail. CMOS does consume current though when it is switching and it also consumes any current that it may need to drive loads, like LEDs, on its outputs.
The principal that any logic function, never mind how large or complicated, can be made from an unlimited number of the two fundamental logic functions: NOR and TWO INPUT AND or TWO INPUT OR, holds true for any binary logic family, even rudimentary relay logic.
Because NAND and NOR gates embody both of theses fundamental logic functions in one chip, it is possible (but not necessarily practical) to make any logical binary function from an unlimited number of TWO INPUT NAND gates or TWO INPUT NOR gates.
Yes, the CD4026 is essentially made from the two fundamental logic functions, and it would be a simple but laborious task for a logic designer, like many on ETO, to make a CD4026 from a bunch of TWO INPUT NAND GATES: CD4011.
But a digital IC designer would not literally use the circuit of the individual chips that you see. Instead, he would have libraries of functions that he would copy and paste to generate a mask to fabricate the chip required in silicon. The reason why he would not necessarily use the circuit of individual chips is that his requirements are different to the requirements for general use. One of the main characteristics being output current drive capability.
To illustrate that more complex logic functions are made up of combinations of the fundamental logic functions have a look at the schematics for the actual CD4026:
https://www.ti.com/lit/ds/symlink/cd4026b.pdf
In general you can stimulate a logic system by:
(1) a DC logic level, either 0 or 1
(2) a momentary pulse, either 0 or 1
(3) an edge, either rising or falling.
Most flip flops, counters, and shift registers are stimulated by an edge of the clock input, invariably the positive edge.
If you are keen to get a feel for digital electronics you best move would be to familiarize yourself with the following chips in order:
(1) Quad TWO INPUT NAND GATE: 74xxx00
(2) Dual D TYPE FLIPFLOP (positive edge clock, asychronous preset and clear. Q and /Q outputs): 74xxx74
(3) FOUR BIT BINARY COUNTER: 74xxx93
(4) EIGHT BIT SHIFT REGISTER (serial in, parallel in, serial out, parallel out): 74xxx299 (the 4 bit 7495 and 74LS395 are simpler to understand but both of theses chips are now obsolete)
(5) Quad TWO INPUT EXCLUSIVE OR GATE: 74xxx86
A flipflop, or bistable (two stable states, either 0 or 1), can be configured as a one bit counter. Counters and shift registers are nothing more than flip flops connected in series with some gating, each flipflop representing one bit. Once you have mastered the 74xxx74 D type flipflop, you will have made a major leap into the field of digital electronics.
You may wonder why the simple 74xxx86 gate is at the end of the list- you will find out.
It is one one the simplest logic chips, but it is capable of some very sophisticated functions, cryptography for example.
Compared to your present academic studies, understanding/designing logic functions should be like falling off a log. A day with a logic designer would do it. There are also a load of excellent books.
One last bit of avuncular advise is to familiarize yourself with basic binary arithmetic and ASCI- all dead easy. Once again, there are some excellent books.
In case you think I am oversimplifying logic design, that is true. It is a vast and very complex field, involving advanced maths of all types and special design techniques, especially to execute logic functions fast. But, what I am saying is that the basics are very simple. Also, digital electronics, both practical and theoretical, is absolutely fascinating, at least I think so.
spec
DATA SHEETS
(1) 74xxx00 NAND gate
**broken link removed**
(2) 74xxx74 D TYPE FLIP FLOP
**broken link removed**
(3) 74xxx93 BINARY COUNTER
**broken link removed**
(4) 74xxx299 SHIFT REGISTER
https://www.ti.com/lit/ds/symlink/cd54hc299.pdf
(5) 74xxx86 EXCLUSIVE OR GATE
**broken link removed**
NOTE: 74HCTxxxx logic chips are high speed CMOS with TTL IO characteristics