4000 series CMOS Logic ICs

General characteristics

• Supply: 3 to 15V, small fluctuations are tolerated.
• Inputs have very high impedance (resistance), this is good because it means they will not affect the part of the circuit where they are connected. However, it also means that unconnected inputs can easily pick up electrical noise and rapidly change between high and low states in an unpredictable way. This is likely to make the IC behave erratically and it will significantly increase the supply current. To prevent problems all unused inputs MUST be connected to the supply (either +Vs or 0V), this applies even if that part of the IC is not being used in the circuit!
• Outputs can sink and source only about 1mA if you wish to maintain the correct output voltage to drive CMOS inputs. If there is no need to drive any inputs the maximum current is about 5mA with a 6V supply, or 10mA with a 9V supply (just enough to light an LED). To switch larger currents you can connect a transistor.
• Fan-out: one output can drive up to 50 inputs.
• Gate propagation time: typically 30ns for a signal to travel through a gate with a 9V supply, it takes a longer time at lower supply voltages.
• Frequency: up to 1MHz, above that the 74 series is a better choice.
• Power consumption (of the IC itself) is very low, a few µW. It is much greater at high frequencies, a few mW at 1MHz for example.

If you are using another reference please be aware that there is some variation in the terms used to describe input pins. I have tried to be logically consistent so the term I have used describes the pin's function when high (true). For example 'disable clock' on the 4026 is often labelled 'clock enable' but this can be confusing because it enables the clock when low (false). An input described as 'active low' is like this, it performs its function when low. If you see a line drawn above a label it means it is active low, for example:    (say 'reset-bar').There are many ICs in the 4000 series and this page only covers a selection, concentrating on the most useful gates, counters, decoders and display drivers. For each IC there is a diagram showing the pin arrangement and brief notes explain the function of the pins where necessary. The notes also explain if the IC's properties differ substantially from the standard characteristics listed above.

The Links page lists some Datasheet websites. 

---

Static precautions

The CMOS circuitry means that 4000 series ICs are static sensitive. Touching a pin while charged with static electricity (from your clothes for example) may damage the IC. In fact most ICs in regular use are quite tolerant and earthing your hands by touching a metal water pipe or window frame before handling them will be adequate. ICs should be left in their protective packaging until you are ready to use them. 

---

Gates

---

Quad 2-input gates

• 4001 quad 2-input NOR
• 4011 quad 2-input NAND
• 4030 quad 2-input EX-OR (now obsolete)
• 4070 quad 2-input EX-OR
• 4071 quad 2-input OR
• 4077 quad 2-input EX-NOR
• 4081 quad 2-input AND
• 4093 quad 2-input NAND with Schmitt trigger inputs

The 4093 has Schmitt trigger inputs to provide good noise immunity. They are ideal for slowly changing or noisy signals. The hysteresis is about 0.5V with a 4.5V supply and almost 2V with a 9V supply. 

---

Triple 3-input gates

• 4023 triple 3-input NAND
• 4025 triple 3-input NOR
• 4073 triple 3-input AND
• 4075 triple 3-input OR

Notice how gate 1 is spread across the two ends of the package. 

---

Dual 4-input gates

• 4002 dual 4-input NOR
• 4012 dual 4-input NAND
• 4072 dual 4-input OR
• 4082 dual 4-input AND

NC = No Connection (a pin that is not used). 

---

4068 8-input NAND/AND* gate

This gate has a propagation time which is about 10 times longer than normal so it is not suitable for high speed circuits.

NC = No Connection (a pin that is not used).

* = The AND output (pin 1) is not available on some versions of the 4068. 

---

4069 hex NOT (inverting buffer)

---

4049 hex NOT and 4050 hex buffer

• 4049 hex NOT (inverting buffer)
• 4050 hex non-inverting buffer

Inputs: These ICs are unusual because their gate inputs can withstand up to +15V even if the power supply is a lower voltage.
Outputs: These ICs are unusual because they are capable of driving 74LS gate inputs directly. To do this they must have a +5V supply (74LS supply voltage). The gate output is sufficient to drive four 74LS inputs.

NC = No Connection (a pin that is not used).

Note the unusual arrangement of the power supply pins for these ICs! 

---

4000 dual 3-input NOR gate and NOT gate

Two 3-input NOR gates and a single NOT gate in one package.

NC = No Connection (a pin that is not used). 

---

Decade and 4-bit Counters

---

4017 decade counter (1-of-10)

The count advances as the clock input becomes high (on the rising-edge). Each output Q0-Q9 goes high in turn as counting advances. For some functions (such as flash sequences) outputs may be combinedusing diodes.
The reset input should be low (0V) for normal operation (counting 0-9). When high it resets the count to zero (Q0 high). This can be done manually with a switch between reset and +Vs and a 10k resistor between reset and 0V. Counting to less than 9 is achieved by connecting the relevant output (Q0-Q9) to reset, for example to count 0,1,2,3 connect Q4 to reset.
The disable input should be low (0V) for normal operation. When high it disables counting so that clock pulses are ignored and the count is kept constant.
The ÷10 output is high for counts 0-4 and low for 5-9, so it provides an output at ¹/₁₀ of the clock frequency. It can be used to drive the clock input of another 4017 (to count the tens).

Example projects: Heart-shaped badge | Network Lead Tester | Traffic Light | Dice | Model Lighthouse 

---

4026 decade counter and 7-segment display driver

The count advances as the clock input becomes high (on the rising-edge). The outputs a-g go high to light the appropriate segments of a common-cathode 7-segment display as the count advances. The maximum output current is about 1mA with a 4.5V supply and 4mA with a 9V supply. This is sufficient to directly drive many 7-segment LED displays. The table below shows the segment sequence in detail.
The reset input should be low (0V) for normal operation (counting 0-9). When high it resets the count to zero.
The disable clock input should be low (0V) for normal operation. When high it disables counting so that clock pulses are ignored and the count is kept constant.
The enable display input should be high (+Vs) for normal operation. When low it makes outputs a-g low, giving a blank display. Theenable out follows this input but with a brief delay.
The ÷10 output (h in table) is high for counts 0-4 and low for 5-9, so it provides an output at ¹/₁₀ of the clock frequency. It can be used to drive the clock input of another 4026 to provide multi-digit counting.
The not 2 output is high unless the count is 2 when it goes low.

Example project: 'Random' flasher for 8 LEDs
This project uses the 4026 in an unconventional way, the outputs a-g and the ÷10 output (h) are used to flash individual LEDs in a complex pattern which appears random if not studied too closely! 

---

4029 up/down synchronous counter with preset

The 4029 is a synchronous counter so its outputs change precisely together on each clock pulse. This is helpful if you need to connect the outputs to logic gates because it avoids the glitches which occur with ripple counters.
The count occurs as the clock input becomes high (on the rising-edge). The up/down input determines the direction of counting: high for up, low for down. The state of up/down should be changed when the clock is high.
For normal operation (counting) preset, and carry in should be low.
The binary/decade input selects the type of counter: 4-bit binary (0-15) when high; decade (0-9) when low.
The counter may be preset by placing the desired binary number on theinputs A-D and briefly making the preset input high. There is no reset input, but preset can be used to reset the count to zero if inputs A-D are all low.

Connecting synchronous counters in a chain: please see 4510/16 below. 

---

4510 up/down decade (0-9) counter with preset
4516 up/down 4-bit (0-15) counter with preset

These are synchronous counters so their outputs change precisely together on each clock pulse. This is helpful if you need to connect their outputs to logic gates because it avoids the glitches which occur with ripple counters.
The count occurs as the clock input becomes high (on the rising-edge). The up/down input determines the direction of counting: high for up, low for down. The state of up/down should be changed when the clock is high.
For normal operation (counting) preset, reset and carry in should be low. When reset is high it resets the count to zero (0000, QA-QD low). The clock input should be low when resetting.

The counter may be preset by placing the desired binary number on theinputs A-D and briefly making the preset input high, the clock input should be low when this happens.

Connecting synchronous counters in a chain
The diagram below shows how to link synchronous counters, notice how all the clock (CK) inputs are linked. Carry out (CO)feeds carry in (CI) of the next counter. Carry in (CI) of the first counter should be low for 4029, 4510 and 4516 counters. 

---

4518 dual decade (0-9) counter
4520 dual 4-bit (0-15) counter

These contain two separate synchronous counters, one on each side of the IC.
Normally a clock signal is connected to the clock input, with theenable input held high. Counting advances as the clock signal becomes high (on the rising-edge). Special arrangements are used if the 4518/20 counters are linked in a chain, as explained below.
For normal operation the reset input should be low, making it high resets the counter to zero (0000, QA-QD low).

Counting to less than the maximum (9 or 15) can be achieved by connecting the appropriate output(s) to the reset input, using an AND gate if necessary. For example to count 0 to 8 connect QA (1) and QD (8) to reset using an AND gate.

Connecting 4518 and 4520 counters in a chain
The diagram below shows how to link 4518 and 4520 counters. Notice how the normal clock inputs are held low, with theenable inputs being used instead. With this arrangement counting advances as the enable input becomes low (on the falling-edge) allowing output QD to supply a clock signal to the next counter. The complete chain is a ripple counter, although the individual counters are synchronous! If it is essential to have truly synchronous counting a system of logic gates is required, please see a 4518/20 datasheet for further details. 

---

7-bit, 12-bit and 14-bit counters

---

4020 14-bit (÷16,384) ripple counter

The 4020 is a ripple counter so beware that glitches may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse.
The count advances as the clock input becomes low (on the falling-edge), this is indicated by the bar over the clock label. This is the usual clock behaviour of ripple counters and it means a counter output can directly drive the clock input of the next counter in a chain.
Output Qn is the nth stage of the counter, representing 2ⁿ, for example Q4 is 2⁴ = 16 (¹/₁₆ of clock frequency) and Q14 is 2¹⁴ = 16384 (¹/₁₆₃₈₄of clock frequency). Note that Q2 and Q3 are not available.
The reset input should be low for normal operation (counting). When high it resets the count to zero (all outputs low).

Also see: 4040 (12-bit) and 4060 (14-bit with internal oscillator). 

---

4024 7-bit (÷128) ripple counter

The 4024 is a ripple counter so beware that glitches may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse.
The count advances as the clock input becomes low (on the falling-edge), this is indicated by the bar over the clock label. This is the usual clock behaviour of ripple counters and it means a counter output can directly drive the clock input of the next counter in a chain.
Output Qn is the nth stage of the counter, representing 2ⁿ, for example Q4 is 2⁴ = 16 (¹/₁₆ of clock frequency) and Q7 is 2⁷ = 128 (¹/₁₂₈ of clock frequency).

The reset input should be low for normal operation (counting). When high it resets the count to zero (all outputs low). 

---

4040 12-bit (÷4096) ripple counter

The 4040 is a ripple counter so beware that glitches may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse.
The count advances as the clock input becomes low (on the falling-edge), this is indicated by the bar over the clock label. This is the usual clock behaviour of ripple counters and it means a counter output can directly drive the clock input of the next counter in a chain.
Output Qn is the nth stage of the counter, representing 2ⁿ, for example Q4 is 2⁴ = 16 (¹/₁₆ of clock frequency) and Q12 is 2¹² = 4096 (¹/₄₀₉₆ of clock frequency).
The reset input should be low for normal operation (counting). When high it resets the count to zero (all outputs low).

Also see these 14-bit counters: 4020 and 4060 (includes internal oscillator). 

---

4060 14-bit (÷16,384) ripple counter with internal oscillator

The 4060 is a ripple counter so beware that glitches may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse.
The count advances as the clock input becomes low (on the falling-edge), this is indicated by the bar over the clock label. This is the usual clock behaviour of ripple counters and it means a counter output can directly drive the clock input of the next counter in a chain. The clock can be driven directly, or connected to the internal oscillator (see below).
Output Qn is the nth stage of the counter, representing 2ⁿ, for example Q4 is 2⁴ = 16 (¹/₁₆ of clock frequency) and Q14 is 2¹⁴ = 16384 (¹/₁₆₃₈₄of clock frequency). Note that Q1-3 and Q11 are not available.
The reset input should be low for normal operation (counting). When high it resets the count to zero (all outputs low).
The 4060 includes an internal oscillator. The clock signal may be supplied in three ways:

• From an external source to the clock input, as for a normal counter. In this case there should be no connections toexternal C and external R (pins 9 and 10).
• RC oscillator as shown in the diagram. The oscillator drives the clock input with an approximate frequency f = ¹/_(2×R1×C) (it partly depends on the supply voltage). R1 should be at least 50k if the supply voltage is less than 7V. R2 should be between 2 and 10 times R1.
• Crystal oscillator as shown in the diagram, note that there is no connection to pin 9. The 32768 Hz crystal will give a 2Hz signal at the last output, Q14.

Also see: 4020 (14-bit) and 4040 (12-bit), neither have internal oscillators.

Example projects: Christmas Decoration | Valentine Heart 

---

Decoders

---

4028 BCD to decimal (1 of 10) decoder

The appropriate output Q0-9 becomes high in response to the BCD (binary coded decimal) input. For example an input of binary 0101 (=5) will make output Q5 high and all other outputs low.
The 4028 is a BCD (binary coded decimal) decoder intended for input values 0 to 9 (0000 to 1001 in binary). With inputs from 10 to 15 (1010 to 1111 in binary) all outputs are low.
Note that the 4028 can be used as a 1-of-8 decoder if input D is held low.

Also see: 4017 (a decade counter and 1-of-10 decoder in a single IC). 

---

7-segment Display Drivers

---

4511 BCD to 7-segment display driver

The appropriate outputs a-g become high to display the BCD (binary coded decimal) number supplied on inputs A-D. The outputs a-g cansource up to 25mA. The 7-segment display segments must be connected between the outputs and 0V with a resistor in series (330with a 5V supply). A common cathode display is required.
Display test and blank input are active-low so they should be high for normal operation. When display test is low all the display segments should light (showing number 8). When blank input is low the display will be blank (all segments off).
The store input should be low for normal operation. When store is high the displayed number is stored internally to give a constant display regardless of any changes which may occur to the inputs A-D.

The 4511 is intended for BCD (binary coded decimal). Inputs values from 10 to 15 (1010 to 1111 in binary) will give a blank display (all segments off). 

Integrated Circuits (Chips)

Integrated Circuits are usually called ICs or chips. They are complex circuits which have been etched onto tiny chips of semiconductor (silicon). The chip is packaged in a plastic holder with pins spaced on a 0.1" (2.54mm) grid which will fit the holes on stripboard and breadboards. Very fine wires inside the package link the chip to the pins.

Pin numbers

The pins are numbered anti-clockwise around the IC (chip) starting near the notch or dot. The diagram shows the numbering for 8-pin and 14-pin ICs, but the principle is the same for all sizes.

IC holders (DIL sockets)

ICs (chips) are easily damaged by heat when soldering and their short pins cannot be protected with a heat sink. Instead we use an IC holder, strictly called a DIL socket (DIL = Dual In-Line), which can be safely soldered onto the circuit board. The IC is pushed into the holder when all soldering is complete.

IC holders are only needed when soldering so they are not used on breadboards.

Commercially produced circuit boards often have ICs soldered directly to the board without an IC holder, usually this is done by a machine which is able to work very quickly. Please don't attempt to do this yourself because you are likely to destroy the IC and it will be difficult to remove without damage by de-soldering.

Removing an IC from its holder

If you need to remove an IC it can be gently prised out of the holder with a small flat-blade screwdriver. Carefully lever up each end by inserting the screwdriver blade between the IC and its holder and gently twisting the screwdriver. Take care to start lifting at both ends before you attempt to remove the IC, otherwise you will bend and possibly break the pins.

---

Static precautions

Many ICs are static sensitive and can be damaged when you touch them because your body may have become charged with static electricity, from your clothes for example. Static sensitive ICs will be supplied in antistatic packaging with a warning label and they should be left in this packaging until you are ready to use them.

It is usually adequate to earth your hands by touching a metal water pipe or window frame before handling the IC but for the more sensitive (and expensive!) ICs special equipment is available, including earthed wrist straps and earthed work surfaces. You can make an earthed work surface with a sheet of aluminium kitchen foil and using a crocodile clip to connect the foil to a metal water pipe or window frame with a 10k resistor in series. 

Datasheets

Datasheets are available for most ICs giving detailed information about their ratings and functions. In some cases example circuits are shown. The large amount of information with symbols and abbreviations can make datasheets seem overwhelming to a beginner, but they are worth reading as you become more confident because they contain a great deal of useful information for more experienced users designing and testing circuits.


The Links page lists someDatasheet websites.

Sinking and sourcing current

IC outputs are often said to 'sink' or 'source' current. The terms refer to the direction of the current at the IC's output.

If the IC is sinking current it is flowing into the output. This means that a device connected between the positive supply (+Vs) and the IC output will be switched on when the output is low (0V).

If the IC is sourcing current it is flowing out of the output. This means that a device connected between the IC output and the negative supply (0V) will be switched on when the output is high (+Vs).

It is possible to connect two devices to an IC output so that one is on when the output is low and the other is on when the output is high. This arrangement is used in the Level Crossing project to make the red LEDs flash alternately.

The maximum sinking and sourcing currents for an IC output are usually the same but there are some exceptions, for example 74LS TTL logic ICs can sink up to 16mA but only source 2mA. 

---

Using diodes to combine outputs

The outputs of ICs must never be directly connected together. However, diodes can be used to combine two or more digital (high/low) outputs from an IC such as a counter. This can be a useful way of producing simple logic functions without using logic gates!

The diagram shows two ways of combining outputs using diodes. The diodes must be capable of passing the output current. 1N4148 signal diodes are suitable for low current devices such as LEDs.

For example the outputs Q0 - Q9 of a 4017 1-of-10 counter go high in turn. Using diodes to combine the 2nd (Q1) and 4th (Q3) outputs as shown in the bottom diagram will make the LED flash twice followed by a longer gap. The diodes are performing the function of an OR gate.

Example projects: Traffic Light | Dice | Model Lighthouse 

---

The 555 and 556 Timers

The 8-pin 555 timer IC is used in many projects, a popular version is the NE555. Most circuits will just specify '555 timer IC' and the NE555 is suitable for these. The 555 output (pin 3) can sink and source up to 200mA. This is more than most ICs and it is sufficient to supply LEDs, relay coils and low current lamps. To switch larger currents you can connect a transistor.

The 556 is a dual version of the 555 housed in a 14-pin package. The two timers (A and B) share the same power supply pins.

Low power versions of the 555 are made, such as the ICM7555, but these should only be used when specified (to increase battery life) because their maximum output current of about 20mA (with 9V supply) is too low for many standard 555 circuits. The ICM7555 has the same pin arrangement as a standard 555.

For further information please see the page on555 and 556 timer circuits. 

---

Logic ICs (chips)

Logic ICs process digital signals and there are many devices, including logic gates, flip-flops, shift registers, counters and display drivers. They can be split into two groups according to their pin arrangements: the 4000 series and the74 series which consists of various families such as the 74HC, 74HCT and 74LS.

For most new projects the 74HC family is the best choice. The older 4000 series is the only family which works with a supply voltage of more than 6V. The 74LS and 74HCT families require a 5V supply so they are not convenient for battery operation.

The table below summarises the important properties of the most popular logic families:

Property	4000 Series	74 Series 74HC	74 Series 74HCT	74 Series 74LS
Technology	CMOS	High-speed CMOS	High-speed CMOS TTL compatible	TTL Low-power Schottky
Power Supply	3 to 15V	2 to 6V	5V ±0.5V	5V ±0.25V
Inputs	Very high impedance. Unused inputs must be connected to +Vs or 0V. Inputs cannot be reliably driven by 74LS outputs unless a 'pull-up' resistor is used (see below).		Very high impedance. Unused inputs must be connected to +Vs or 0V. Compatible with 74LS (TTL) outputs.	'Float' high to logic 1 if unconnected. 1mA must be drawn out to hold them at logic 0.
Outputs	Can sink and source about 5mA (10mA with 9V supply), enough to light an LED. To switch larger currents use a transistor.	Can sink and sourceabout 20mA, enough to light an LED. To switch larger currents use a transistor.	Can sink and sourceabout 20mA, enough to light an LED. To switch larger currents use atransistor.	Can sink up to 16mA (enough to light an LED), but source only about 2mA. To switch larger currents use a transistor.
Fan-out	One output can drive up to 50 CMOS, 74HC or 74HCT inputs, but only one 74LS input.	One output can drive up to 50 CMOS, 74HC or 74HCT inputs, but only 10 74LS inputs.		One output can drive up to 10 74LS inputs or 50 74HCT inputs.
Maximum Frequency	about 1MHz	about 25MHz	about 25MHz	about 35MHz
Power consumption of the IC itself	A few µW.	A few µW.	A few µW.	A few mW.

Driving 4000 or 74HC inputs from a 74LS output using a pull-up resistor.

Mixing Logic Families

It is best to build a circuit using just one logic family, but if necessary the different families may be mixed providing the power supply is suitable for all of them. For example mixing 4000 and 74HC requires the power supply to be in the range 3 to 6V. A circuit which includes 74LS or 74HCT ICs must have a 5V supply.

A 74LS output cannot reliably drive a 4000 or 74HC input unless a 'pull-up' resistor of 2.2k is connected between the +5V supply and the input to correct the slightly different logic voltage ranges used.

Note that a 4000 series output can drive only one 74LS input. 

---

Quick links to individual ICs4000    4060 4001    4068 4002    4069 4011    4070 4012    4071 4017    4072 4020    4073 4023    4075 4024    4077 4025    4081 4026    4082 4028    4093 4029    4510 4030    4511 4040    4516 4049    4518 4050    4520

4000 Series CMOS

This family of logic ICs is numbered from 4000 onwards, and from 4500 onwards. They have a B at the end of the number (e.g. 4001B) which refers to an improved design introduced some years ago. Most of them are in 14-pin or 16-pin packages. They use CMOS circuitry which means they use very little power and can tolerate a wide range of power supply voltages (3 to 15V) making them ideal for battery powered projects. CMOS is pronounced 'see-moss' and stands for Complementary Metal Oxide Semiconductor.

However the CMOS circuitry also means that they are static sensitive. Touching a pin while charged with static electricity (from your clothes for example) may damage the IC. In fact most ICs in regular use are quite tolerant and earthing your hands by touching a metal water pipe or window frame before handling them will be adequate. ICs should be left in their protective packaging until you are ready to use them. For the more sensitive (and expensive!) ICs special equipment is available, including earthed wrist straps and earthed work surfaces.

For further information, including pin connections, please use the quick links on the right or go to 4000 Series ICs. 

---

Quick links to individual ICs7400    7432 7402    7442 7403    7447 7404    7486 7405    7490 7408    7493 7409  74132 7410  74160 7411  74161 7412  74162 7414  74163 7420  74192 7421  74193 7427  74390 7430  7439374HC4017 74HC4020 74HC4040 74HC4060 74HC4511

74 Series: 74LS, 74HC and 74HCT

There are several families of logic ICs numbered from 74xx00 onwards with letters (xx) in the middle of the number to indicate the type of circuitry, eg 74LS00 and 74HC00. The original family (now obsolete) had no letters, eg 7400.

The 74LS (Low-power Schottky) family (like the original) uses TTL (Transistor-Transistor Logic) circuitry which is fast but requires more power than later families.

The 74HC family has High-speed CMOS circuitry, combining the speed of TTL with the very low power consumption of the 4000 series. They are CMOS ICs with the same pin arrangements as the older 74LS family. Note that 74HC inputs cannot be reliably driven by 74LS outputs because the voltage ranges used for logic 0 are not quite compatible, use 74HCT instead.

The 74HCT family is a special version of 74HC with 74LS TTL-compatible inputs so 74HCT can be safely mixed with 74LS in the same system. In fact 74HCT can be used as low-power direct replacements for the older 74LS ICs in most circuits. The minor disadvantage of 74HCT is a lower immunity to noise, but this is unlikely to be a problem in most situations.

Beware that the 74 series is often still called the 'TTL series' even though the latest ICs do not use TTL!

For further information, including pin connections, please use the quick links on the right or go to74 series ICs.

The CMOS circuitry used in the 74HC and 74HCT series ICs means that they are static sensitive. Touching a pin while charged with static electricity (from your clothes for example) may damage the IC. In fact most ICs in regular use are quite tolerant and earthing your hands by touching a metal water pipe or window frame before handling them will be adequate. ICs should be left in their protective packaging until you are ready to use them. 

---

PIC microcontrollers

A PIC is a Programmable Integrated Circuit microcontroller, a 'computer-on-a-chip'. They have a processor and memory to run a program responding to inputs and controlling outputs, so they can easily achieve complex functions which would require several conventional ICs.

Programming a PIC microcontroller may seem daunting to a beginner but there are a number of systems designed to make this easy. The PICAXE system is an excellent example because it uses a standard computer to program (and re-program) the PICs; no specialist equipment is required other than a low-cost download lead. Programs can be written in a simple version of BASIC or using a flowchart. The PICAXE programming software and extensive documentation is available to download free of charge, making the system ideal for education and users at home. For further information (including downloads) please see www.picaxe.co.uk

If you think PICs are not for you because you have never written a computer program, please look at the PICAXE system! It is very easy to get started using a few simple BASIC commands and there are a number of projects available as kits which are ideal for beginners. The system is stocked byRapid Electronics. 

---