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PIC FAQ

PIC FAQ (Frequently Asked Questions)

What is a PIC?

A PIC is Peripheral Interface Controller. Other people have called them other things such as Programmable integrated circuits and Peripheral Integrated Controllers amongst others, but Peripheral Integrated Controller is considered the correct name, and it does exactly that. ‘It does what it says on the tin’. It controls peripherals. It is a controller. It is an integrated circuit that controls other integrated circuits or transistors or relays or LEDs or triacs and probably more. They can be found in domestic washing machines to control the washing sequence. Dishwashers use them as well. Some coded car locks have a PIC embedded in a key fob that controls the RF signal.

What are they used for?

These devices are used when circuit complications and cost would not allow the use of logic devices. It is possible to replace tens of logic gates with just one of these micro controller chips (PICs). They can be used to turn-on appliances and to remember their last and indeed all of their instructions. The PICs we are using in this publication operate at speeds of 4 MHz. Although there are others that operate at much faster speeds.

What are the advantages?

One of the advantages of using a 16C84 and 16F84, is that they are re-programmable. This is easily done by simply writing over the last set of data. This automatically erases the last data entered. There is no need to erase first, although it may be prudent to do so in the event of programming frequently. The PIC is also reasonably priced at around £2 each from Crownhill Associates Ltd and other suppliers. These devices work with a maximum 5 volts. Our test prototypes and even finished projects use 4.5 volts and even as low as 3 volts. The power consumption is also very low.

What are their limitations?

I don’t know of any that will stop me from using them!!

How do you use them?

This is a difficult question, as it could be asking anything. I will try to answer by saying that they need a 5-volt (up to) supply and they have to be programmed with the aid of a computer. The software is freely available (PICBASIC compiler, however is a commercial product and is available from Crownhill of Cambridge) and is simple to use, as will be found in the ‘practical’ chapters.

How do you program them?

They are programmed with the aid of a computer. This can be an old XT or AT type. A 286, 386 and 486 computers have been used by Jasper and me, as well as the faster Pentium types. It does not matter what machine you have as long as it can load the software. In this book the compiling software is PICBASIC as the emphasis, and the programmers are either serial port or parallel port types depending on the computer used. Whatever Type of programmer is used, the PIC is programmed serially, i.e. one bit at a time. The speed of the computer doesn’t seem to make much difference to the programming time. Although, the compiling time, when using PICBASIC, is greatly increased with a fast Pentium compared to the older, slower machines. But we are talking fractions of a minute, and not yards or miles!

How much are they?

The prices vary quite considerably from supplier to supplier. The cheapest, and a reliable source, is Crownhill Associates Ltd. This company sells them for about £2 each.

How reliable are they?

I have been using these PIC devices for many years, without ‘blowing’ them up. I have even reversed-polarity them, by mistake (of course!), and when correcting the fault, they have carried on working again after they had cooled !

How easy is it to alter the program?

That’s simple, you just write over them.

How many times can you program them?

How many times do you want to? Is my reply, but apparently, about a hundred thousand times, and I may have even done that!! Jasper probably has as well!!