March 1999 49

E mbedded microprocessor devel-opment can seem to be an ex-pensive task, requiring lots ofspecialized equipment that is

beyond the means of most amateurs. Al-though developing projects using PIC1 mi-croprocessors can be expensive, it doesnthave to be. PIC development can be done withjust a handful of parts: an EPROM eraser,some kind of programming language and alow-cost PIC programmer.2 Thats an exactlist of the equipment that I use. I dont haveaccess to specialized professional equip-ment, but I do develop many useful projectswith PICs.3,4

Why Pick PICs?PICs are an enabling technology. All

those logic, control, communication and dis-play functions that our projects need can bepacked into a single chipa chip that can bereconfigured at your pleasure! Similarly, wecan add features to our projects that makethem even more professional and easier tooperate.

The simplest, popular PICs are containedin a single 18-pin package, have 13 I/O pinsand need only an external clock for opera-tion. For usefulness, the PIC is truly the 90sversion of the venerable 555 timer!

Most of the PICs you likely will beusing are flash EEPROM or windowedEPROMs. This means that they can be pro-grammed over and over again. In fact, thelegs on my frequently used PICs break offlong before the write/erase cycle limit of thePIC is ever reached! In higher-volume com-mercial applications, PICs are available atlower cost in a one-time programmable(OTP) version. The OTP version allowsthe code to be burned into the PIC once. Ob-viously, this cheaper device wouldnt becheaper to use when youre developingnew code, but when the code is stable, a

By Steve Hageman

1Notes appear on page 51.

commercial manufacturer may choose touse OTP versions to reduce cost.

Basic PIC UsesI break PIC applications up into two over-

lapping categories: Stand-alone applications such as CW

keyers, ID modules, etc. These PIC appli-cations use the device as a programmablelogic array (PLA). That is, the programyou write for the PIC can take the place ofhundreds of discrete logic gates. Suchprojects usually stand by themselves andhave simple user interfaces that may in-clude an LCD (see the sidebar SimpleProject Displays) and some user-interac-tion switches. My 2-meter PC-controllableFM receiver (see Note 4) is an example ofthis type of application.

The other application category involvesusing the PIC as a PC interface. Becausethe PIC can communicate easily usingRS-232 connections, you can use a PIC asa sophisticated programmable UART.This follows the electronics industry trendtoward virtual instruments (VI), that is,electronic equipment that does not have aphysical front panel, but a communica-tions interface to a computer that pro-cesses the instruments data and displaysthe instruments virtual front-panel con-trols. My Personal Network Analyzer (seeNote 3) is one example of such a project.5The two PIC-usage categories may over-

lap, as they do in my 2-meter receiver. Thatproject uses a PIC to operate a user interface,including an LCD, knobs and switches. Whenit detects the presence of an RS-232 connec-tion, it operates like a virtual radio with a PCcontrolling the receiver.

PC Control of a Virtual InstrumentThe key to operating a virtual instrument

is the program running on the PC. MS-DOS isa simple environment in which to operate,

PIC Developmenton a ShoestringAre you itching to develop PIC-basedprojects yourself? Here are someideas on how to go about it.

but the availability of DOS-based develop-ment tools is nonexistent now, except forshareware. This leaves Windowsand thetools here are quite good. Microsofts VisualBasic is a very reliable and useful develop-ment tool. You may be able to find someonesold copy of Visual Basic 3 for Windows 3.1 or95 development. Or, if you want to start withthe latest 32-bit versions, use Visual Basic 5or 6 for Windows 95/98 programming.

Because each PC-based language uses itsown way of controlling the serial port, itsimpractical to list them all here. But, the se-rial port is a commonly supported communi-cation method under DOS and Windows, soits a part of all these languages. Check thelanguage manuals and help files for morespecific information.

For an example of the PIC code thatcontrols a virtual instrument via RS-232, visitmy Web page describing the Personal Net-work Analyzer project and download thePIC source code.

Which PICs to Use?At first, you seem to be faced with a bewil-

dering array of PICs from which to choose.Your choice of which PICs to use may wellstart with the language youll be using and/orwhat your programmer can support. I use fourdevices for all of my fun projects: the mid-range 16C6x, 16F84 and 16C7x; this keepscosts down and ensures I will always havedevices available when I need them. Here arethe reasons I chose these devices:

16F84A low cost 18-pin device withmoderate memory size (1 kB). This deviceis used for basic control applications thatwont be large, need analog input (ie, anADC) or use a lot of I/O pins (My Web site6shows several robots that my kids and I have

Ready for another programmingassignment! My shoestring developmentstation includes a Microchip programmer,an EPROM eraser and, of course, a PC.

50 March 1999

Figure 1My universal RS-232 debugging cable simply clips to the circuit Im testing.Three leads are all that is required to get bidirectional communication from a PICbreadboard to any PC terminal program.

built with this device). This is the mostpopular hobbyist PIC of all time (an olderdevice was called the 16C84). This deviceuses flash memory and does not need to beerased in an EPROM eraser before it can bereprogrammed.

16C71Like the 16F84, but it also has abuilt-in four-channel, 8-bit ADC. This deviceis used where I need to get analog signals intothe PIC for control applications (such as thePersonal Network Analyzer; see Note 3). Thenewest replacement to this device is the16C711.

16C63This device is in a 28-pin pack-age, contains one five-bit I/O port and two8-bit I/O ports. The device also has a hard-ware UART and 4 kB of memory. I use thisdevice where I need the execution speed ofthe built in UART, the extra ports or the 4 kBof memory for large, complicated projects.

16C73Like the 16C63, but also has abuilt-in, four-channel, ADC like the 16C71. Iuse this device in all the applications a 16C63would be used for, but also need an ADC.

With just these four devices, I can keepmy investment low and put together nearlyany project I likely have the time for! To pro-gram these PICs, I use a Microchip PicStartprogrammer.7 Its a bit on the expensive side,but it can program all of the currently avail-able PICs.

How to Program a PICProgramming a PIC is no harder than writ-

Figure 2This simple adapter cable allows easy debugging of PIC applications with anyPC-based terminal program. Employing clip leads makes it easy to do on-the-spotdebugging and probing of the inner workings of your PIC programs. You will want tomake one of these early on, because you wont feel like making it when you really need it!

ing a small program for a PC; the exact se-quence of steps is different, but its not diffi-cult to learn. If you want to program in as-sembly language, the tools are free fromMicrochip.8 Programming in higher-levellanguages such as BASIC and C can be ac-complished using low-cost (under $100)tools.9,10 These higher-level language toolsare usually referred to as compilers becausethey take the high-level statements and com-pile them into processor-specific machinelanguage. I program my projects in C, a high-level language that keeps the code close tothe hardware. This is the perfect language touse to talk to a PIC because controlling hard-ware is the whole idea. However, BASIC isalso a viable language to use for amateurprojects.

Once a program is written (in whateverlanguage you have chosen), the assembleror compiler generates a binary image of thetarget PICs memory. This image file is usu-ally called a hex file, because it is in a formatcalled the Intel hex 8 format. You dont needto know the technical details of this formatfor successful application of the PIC.Microchips tools produce this format, somost of the low-cost programmers availablesupport it as do the compiler manufacturers,and its become the de-facto standard forPICs. All you really need to know is how toload the image file into your programmerand download it to your PIC, usually asimple task.

Debugging an ApplicationDebugging is where the fun startsand

stops, sometimes! The need for debugging canarise for two basic reasons: Because the pro-gram doesnt appear to work as you planned,or because you think up features to add asyoure writing the programs. Professionalsmay debug with expensive in-circuit emula-tors (ICE systems) that allow steppingthrough the code line by line while connectedto the target hardware. Although this is themost effective way to see how the programactually works from a time standpoint, its costis usually beyond the means of most amateurs.

Debugging Tip 1I use a slightly less time-effective debug-

ging method than ICE, but its a lot friendlierto your pocketbook! Most applications arebest built in stages. Each stage adds a func-tion, and I fully test that function before add-ing the next one. This way, the potential prob-lem areas are kept small. If the program stopsworking after a new stage is added, then Iknow to look at the new stage first! Some-times problems can be found by observingthe action of the hardware and looking at thesource code again. More often than not,youll spot an obvious error and be able tocorrect it.

In fact, the programs for my 2-meter re-ceiver project are built exactly this way. Inpast projects, I have used LCDs, so I reusedthis already-tested code to display programoutput when testing the other hardware code(described later). I had also used the PICsbuilt-in ADC and RS-232 UART, so thesecontrolling subroutines were reused. I had notused an interrupt-driven rotary encoder be-fore with a PIC, so I wrote some simple pro-grams to experiment with how to best do this.I even used a 16C84 processor for this devel-opment because I had a breadboard alreadybuilt up and wanted to reuse that also. WhenI had the encoder working correctly, I addedthe switch inputs and worked on debouncingroutines and getting the RC networks con-nected to these switches properly.

When all the lower-level hardware-con-trol routines were built and tested, I startedbuilding the final application safe in theknowledge that when my program said reada debounced switch, if the program didntwork, I knew it was the main programs logicand not the previously written and tested sub-routines. This is, in fact, my first approach todeveloping PIC applications: Work on thehardware-control stuff in small increments.It saves time in the long run.

Debugging Tip 2My second approach to debugging on a

shoestring is simply to keep five or more PICsin an EPROM eraser at all times. Doing soallows me to execute almost instantaneouswrite, compile, program, test cycles. Manytimes during development, I may work with apiece of code for only a few minutes before Idecide it needs improvement. Sometimes, itjust doesnt run at all! Being able to immedi-ately get another blank PIC into the pro-

March 1999 51

grammers socket keeps the developmentcycle short and productive (much like it ison a PC). This also saves time in the long runat the minor expense of having a few extraPICs lying around.

Debugging Tip 3My third and last debugging tip is to use

an RS-232 link to a PC during development,to show what is happening inside the PICduring program execution. In the early stagesof development, I usually use the LCD (if theproject has one) to show what is happening inthe program. I write to the display much likeyou would use PRINT statements in BASICto print the values of internal variables, orjust to print out where the program is whileits running.

As I get farther along in writing thesoftware, Ill likely have the LCD tied into themain program, so its not convenient to usethe LCD for debugging any more. At thatpoint, I switch to using an RS-232 link to aPC. All of the better programming languageshave built-in RS-232 serial commands thatcan be used on PICs with or without UARTs.My compiler recognizes nonUART devicesand automatically adds software routines thatperform the RS-232 input and output. Theseroutines may take up a little of your codespace, but they really help debugging.

In its simplest form, an RS-232 link onlyuses one PIC pin. The C compiler I use canconfigure any I/O pin for RS-232 I/O, andthere is usually one pin available for debug-ging purposes. The PICs RS-232 pin is con-nected to the PCs RS-232 receive pin, aground wire is added to connect the PCsground to the PICs and off we go! (See Fig-ure 2). Using any terminal program (Windowsor DOS, configured for the right number ofbits and data rate), the data from the PIC canbe viewed as the program executes. If youneed to pause the program at various points,you can add an RS-232 input to another of thePICs pins and use it to have the PIC waituntil it receives a character from the terminalprogram.11

Using RS-232 for debugging really rein-forces Debugging Tip 2. That is, you willprobably be making rapid changes to the pro-gram as you move debugging PRINT state-ments around, and you want to keep your ef-ficiency high. You wont want to wait whileanother PIC is erased before trying the nextexperiment. So, keep plenty of PICs roastingin the EPROM eraser at all times! Im notsuggesting that you keep hacking code untilit seems to work! Even the most experiencedprofessionals learn by doing. Im saying thatwhile learning more by doing more, youkeep your debugging efficiency high.

For your next project, you can probablyreuse much of the code that you developedfor previous projects and speed your devel-opment time even more. As I mentioned ear-lier, thats how I develop many of the piecesfor my projects.Notes1Microchip Technology Inc, 2355 W Chandler

Blvd, Chandler, AZ 85224-6199; tel 602-786-

Figure BThese simple-to-usecharacter-based displays really givea professional appearance to ourprojects. They can be programmedserially themselves, or connecteddirectly to a PIC through six I/O pins.

Figure ABy using an LCDs four-bitnibble mode, the number of I/O pinsrequired for operation are reduced tosix.

Simple Project DisplaysYou may notice many articles nowa-

days that include LCDs. Available frommany manufacturers, LCDs are reallycomplete display subsystems.* Theyare commonly programmed in four-bitnibbles and can display the full upper-and lowercase ASCII character set.

Different display models are avail-able ranging from 16 character andone line to 40 characters and fourlines. LCD costs start at under $20.The displays are 14 pin devices, with11 pins to deal with when program-ming. LCDs have an 8-bit mode and a4-bit mode. In 4-bit mode, you onlyneed four data lines and two controllines to completely control the display;see the accompanying figure. Usingthe four-bit mode saves on I/O pins,which with a PIC, is usually important(see Figure A).

Although it is relatively easy to pro-gram these displays, it can be madeeven easier by buying one of the manyadd-on serial adapters. These serialadapters allow the display to be ac-cessed with serial bit streams from asingle PIC pin. Interestingly enough,these serial adapters are themselvesusually built with PIC microprocessors!

Using one of these displays boils

down to three simple functions: Initialize the display; this clears the

entire display. Set the line (ie, the first, second, etc)

to write to. This also sets the cursorto the beginning of the line.

Write text to the display. You can writesingle characters or entire strings tothe display. The display itself takescare of positioning each character.

Translated into C code, these state-ments look like this:

init_lcd();// Initialize and clear the LCD Display

first_line();// Set cursor to first line

write_lcd(Hello World...);// Write something

second_line();// Set cursor to second line

write_lcd(QST is the best);// Write something else

The result can be seen in Figure B.These are exactly the functions I in-

clude in my PIC projects that use theLCDs. For an example of the codeused to drive a display, see my2-meter FM receiver Web page.Steve Hageman

*For example, see the Optrex character dis-plays available from Digi-Key and others(Digi-Key Corp, 701 Brooks Ave S, ThiefRiver Falls, MN 56701-0677 tel 800-344-4539, 218-681-6674; fax 218-681-3380http://www.digikey.com).

Serial Backpak from Scott Edwards Elec-tronics, http://www.seetron.com

ht tp : / /www.son ic .ne t /~shageman /2_meter.html

7200, fax 602-899-9210; http://microchip.com.

2See John Hansen, W2FS, Using PICMicrocontrollers in Amateur Radio Projects,QST, Oct 1998, pp 34-40.Ed.

3Steve Hageman, Build Your Own NetworkAnalyzerPart 1, QST, Jan 1998, pp 39-45;Part 2, QST, Feb 1998, pp 35-39.

4Steve Hageman, A 2-Meter FM Receiver withPC Control, QST, Feb 1999, pp 35-40.

5http://www.sonic.net/~shageman/pna.html6http://www.sonic.net/~shageman7See Note 1.8microEngineering Labs, Inc, Box 7532, Colo-

rado Springs, CO 80933, tel 719-520-5323;fax 719-520-1867; http://www.melabs.com.

9See Note 6.10CCS PCM, A C compiler for mid-range PICs

is available at http://www.ccsinfo.com.11Be sure to note that since we are not using

any handshaking lines with the RS-232 con-nection, set your terminal programs hand-shaking parameters to none, or as it is some-times called, no flow control.

You can contact Steven Hageman at 9532Camelot Dr, Windsor, CA 95492; shageman@sonic.net.