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AT LAST: A SIMPLE, CHEAP, EFFECTIVE, D-I-Y, PIC PROGRAMMER With few exceptions, designs published in SILICON CHIP have steered clear of PIC microcontrollers because of the difficulty home constructors have had in programming them. All that is about to change ... change... DESIGN BY MICHAEL A. COVINGTON* ARTICLE BY ROSS TESTER 34  Silicon Chip F IRST OF ALL, we should deBoth the flash program memory most popular PIC, the 16F84 (and scribe the PIC microcontroller and the EPROM inside the PIC can be with very minor program mods, the because many readers might erased and re-programmed so, within 16F83 and 16C84). When we say simthink they haven’t come across them reason, you can keep on using the ple, we mean just that. It contains no before. That is almost certainly not same chip over and over. In fact, the specialised components, it connects true, because these days there is flash program memory is only guaran- to the printer port of any PC running hardly an electronic device which teed for 1000 erase/write cycles while freely downloadable software, and it’s doesn’t have a microcontroller buried the EPROM is guaranteed for just a inexpensive: the whole kit including somewhere in it. And a huge number few more cycles – ten million, in fact! a PIC 16F84 sells for less than $30. of those would be PICs. Of course, there are many other This project first appeared in the But using and/or programming microcontrollers but it is the PIC September 1998 edition of the US the PIC as a device in its own right? which has captured most attention magazine, “Electronics Now”. The auWe agree, that’s an entirely different in the d-i-y market because of its thor, Michael A Covington, described matter. Again, though, just what is price and ease of use. It is made by his project as a “no parts” PIC proa PIC? Come to think of it what is a Microchip Inc in the USA and a lot grammer because of the very few extra micro-controller? more information about PICs can be bits needed. Much of the text in this obtained from their website, www.mi- article is adapted from the original. It is a tiny computer, complete with crochip.com – it’s well worth a visit. Michael also acknowledged the work CPU, ROM, RAM and I/O circuits all A word to the wise: be careful about of David Tait in England in producing on the one chip. There are various downloading if you’re on a time- or a PIC programming package called versions of the PIC microcontroller, megabyte-based ISP. The PIC16F8X “TOPIC”, of which this programmer is the most common (for our purposes) a direct descendant. being the 16 series: 16F84 (the most popular, with Also described 68 bytes of RAM and 1024 in the article was a words of program memory companion “demo” in “flash” EEPROM which circuit of an 8-LED can be rewritten at least a chaser (partly as a million times); the 16C84 learning aid but also (similar but with an older handy for checking type of EEPROM); and that the main prothe 16F83 which has only ject worked). Branhalf the memory of its big co Justic, of Oatley brothers. Electronics, saw the project and liked We will concentrate on the idea – and its the 16F84 (even though this simplicity. He also project will also program knew it would be the 16C84 and 16F83). It much more popular operates from a supply if based on a PC anywhere from 4V to 6V board rather, than (some versions work down Pin connections for the 16F84 PIC from Microchip, Inc. Pins 1-3, the Veroboard used to 2V!) and there are 13 pins 6-13 and 17-18 are all input or output ports, depending on what by the original. which can be either inputs the program tells them to be. or outputs. So he designed a board for not only the These PICs are extremely programmer but also the chaser. While versatile little chips, capable of being data sheet pdf file alone is 124 pages long (1.35MB) – and the MPLAB pro- both the programmer and chaser are programmed (in assembly language, on the one board, they are easily sepbut don’t let that scare you!) to do an gram is over 8MB.) (For more background on PICs, arated. Therefore the programmer and enormous range of tasks. What’s more, refer to the article in the August 1994 chaser can be operated independently, the program will stay in memory for a issue. Though now rather dated as far if you want. guaranteed 40 years. As an old friend as devices are concerned, the basic of SILICON CHIP often says, “It’ll see All of that resulted in the project information is still current). me out . . .” presented here: a simple, cheap but A PIC microcontroller also formed effective PIC programmer. If you’ve What sort of tasks? Virtually anything capable of being switched, the “heart” of the BASIC Stamp pro- ever thought about getting into PICs, controlled, measured, actuated, com- ject (January 1999) – the big advantage this is the way to do it! of using a PIC alone, of course, is the pared. . . You’ll find PICs in everything Getting the data in difference in cost. The downside (at from the mouse attached to your least until now) has been the difficulty computer to the car you’re driving, We keep talking about ease of use. from microwave ovens to washing in programming the PIC. So how do you use a PIC? How do you machines, from digital clocks to inget your program into it? The PIC programmer ter-stellar rockets. Well, maybe not It’s quite simple: with power apinterstellar rockets . . . but you get And that brings us to this project. plied to the PIC, the voltage on pin 4 the picture. It’s a very simple programmer for the is raised to between +12V and +14V. MARCH 1999  35 taking D2’s anode low. This turns off D2, blocking current flow. The PIC chip is then free to receive data from pin 14 of the printer port, with the programming voltage switched by transistor Q1. The connection that D1 creates between printer port pins 11 and 17 lets the programming software detect if the programmer is connected to the port. There are also two LM317 regulators – one of which is a fixed 13V supply while the other is a variable 4-6V supply which covers the 5V rail. Both of these are powered from a nominal 13.8VDC plugpack which actually supplies around 17-18V. Fig.1: the PIC Programmer, which plugs into your PC via its parallel You might be wondering port (printer) socket. IC1 is the PIC actually being programmed. why the second supply is variable, not fixed at 5V Data is then clocked in one bit at a PC can read data from pin 13 of the which, of course, would be easier. It’s time into pin 13. As each bit goes in, PIC through pin 11 of the printer port. variable to allow reliability checking the voltage on pin 12 is raised to +5V OK, we’ve got that far. But where of the data – but more of this anon. for at least 0.1µs (yes, microsecond!) does that data going into the PIC If plugging the DB25 connector before being sent low (0V) again. come from? directly into your computer’s paralThe data stream going into pin 13 That’s the job of this little program- lel port is inconvenient or difficult, contains both the commands that mer. In conjunction with virtually any you can use a suitable DB25-male to specify the various steps in the pro- PC with a parallel port and suitable DB25-female parallel printer extengramming process, as well as the data (free!) programs, the programming sion cable. But make sure that it is itself that will be stored in the chip. data and clock signals are applied to not a serial cable – some of these are The PIC can also send its contents the appropriate PIC pins at the right not wired “straight through” but have back out through pin 13 to verify that time. We’ll get to the programs in a crossovers built in. it has stored the correct data. When moment. Before moving away from the cirpin 17 of the printer port is high, the cuit diagrams, Fig. 2 shows the PIC The circuit demonstration circuit. This simply Refer now to Fig. has eight LEDs with current-limiting 1 – the PIC program- resistors connected to eight of the 13 mer circuit diagram. I/O ports. The “demo.asm” file proAs you can see, when grams the PIC to make the LEDs chase we claimed it was each other, wait a short time, then start simple we weren’t again, ad infinitum. kidding: just two Such a chaser could be made with s t e e r i n g d i o d e s , an oscillator/pulse generator and a a transistor and a counter, probably at a much lower sprinkling of pas- cost than this demonstration circuit. sive components and But look at the component count on that’s about it. the demo board: just the PIC, a supThe diodes are ply bypass capacitor, an R/C circuit used to sense when which generates the pulses (using the data is going from PIC itself) and nothing else except the the PIC back to the LEDs and their series resistors! All the PC. R1 & D2 provide work is done by the PIC. pull-up for the data What’s more, if you want to change signal. When pin 17 the chase pattern, the timing or any The completed PIC Programmer, shown separated from of the printer port is other factor in this version, it’s just the demo PC board. As you can see, the number of low, D1 conducts, a matter of re-programming. With components is small. 36  Silicon Chip Fig.2 (left): the circuit of the add-on PIC demonstration board which is an 8-LED chaser. The separated chaser PC board is shown at right. As supplied, the chaser board will be attached to the PIC programmer PC board (as shown on the opening page and in the component overlay below). There is no reason to separate these boards unless you have a reason to do so. The chaser will confirm your PIC Programmer is working properly and you can always re-use the PIC. conventional chaser circuits, you’re up for a new PC board and probably additional components. Both the programmer and chaser have been combined on one PC board, the component overlay of which is shown in Fig.3. Construction Because of the few components, construction is relatively straightforward. Just keep in mind that many of the components are polarised, including the LEDs. These all mount the same way down the edge of the PC board – so if one looks different to the others, it’s probably back to front. Speaking of different, the prototype chaser had four different LED colours – red, yellow, green and orange. While this looks pretty, we reckon it tends to spoil the “chase” effect. Hopefully kits will have all the one colour LED. The DB25 socket is soldered directly to the PC board, not forgetting the shell earthing pins at each end. Like the IC sockets, spacing of the DB25 pads is pretty close so you’ll need a fine iron and a good light. Check and double check that you haven’t bridged any pads together. The PIC chip(s) should be left until last and inserted into their sockets only after you have thoroughly check­ ed your component placement and soldering. In fact, it’s probably a good idea to do a voltage check prior to inserting the PIC: the two wire links make excellent test points. There should be about 13V between the link alongside C5 and the shell of the DB25 socket and there should be somewhere Fig.3: the component overlay for both the PIC programmer and demonstration chaser, in this case together on one PC board. If you do decide to separate them, it’s best to do it before assembly and soldering! between 4V and 6V (depending on the setting of VR1) between the link below R8 and the DB25 shell. If you get these figures (or close to them) turn off the power, ready for insertion of the PIC. If not, send out the search party for your mistake or poor solder joint! It’s important to have all the pins of the PIC straight and lined up with the holes in the socket before insertion. Many a time we’ve seen projects not working because one pin is folded up under the IC, or missed the socket entirely and gone down the side! The notch (or dot) on the PIC goes towards the top of the PC board when held with the DB25 socket on the left (ie, so the printing on the PC board reads correctly). The software you need Now we come to the good bits (sorry about the pun!) – actually writing a PIC program, compiling it and “burning” the program into the PIC’s memory. The easiest way to learn to use the programmer is to write a simple program, in this case, the LED Chaser. That’s why space for the chaser is included on the PC board. The program is first written in assembly language. Unfortunately, a primer on assembly is outside the scope of this article but for those who don’t know anything about assembly language, we’ve listed the code for the chaser (demo.asm) in Listing 1. You can either type in the code in any text editor or word processor or MARCH 1999  37 ; File DEMO.ASM ; Assembly code for PIC16F84 microcontroller ; Blinks LEDs on outputs in a rotating pattern. ; With 75-kHz osc, each LED stays on 1/2 second. ; CPU configuration ; (It’s a 16F84, RC oscillator, ; watchdog timer off, power-up timer on) processor 16f84 include <p16f84.inc> __config _RC_OSC & _WDT_OFF & _PWRTE_ON ; Declare variables at 2 memory locations J equ H’1F’ ; J = address hex 1F K equ H’1E’ ; K = address hex 1E ; Program org 0 ; start at address 0 ; Set port B as output and initialize it movlw B’00000000' ; w := 00000000 binary tris PORTB ; port B ctrl register := w movlw B’00000001' ; w := 00000001 binary movwf PORTB ; port B itself := w ; Rotate the bits of port B leftward mloop: rlf PORTB,f ; Waste some time by executing nested loops movlw D’50' ; w := 50 decimal movwf J ; J := w jloop: movwf K ; K := w kloop: decfsz K,f ; K = K-1, skip next if zero goto kloop decfsz J,f ; J = J-1, skip next if zero goto jloop ; Do it all again goto mloop end Listing 1: the listing of demo.asm, ready for compiling. It can also be downloaded – see panel at the end of this feature. you can download the listing (see panel). We've also printed the PIC 16XFX instruction set and opcode field descriptions to give you a better understanding. Incidentally, while on the subject of downloading, two items of software are needed to use the PIC programmer. That’s the bad news. The good news is that both are free! The first of these is a program called “MPLAB” and is just one of the goodies available from the Microchip website (www.microchip.com). Designed to operate under Microsoft Windows, it’s a full-featured development program for compiling and testing PIC programs. MPLAB is called an assembler: it lets you edit assembly-language programs (also called source code), assemble them into object code, then step through the resulting binary code to see if it will actually work in the microcontroller. This is before you’ve committed any code to the PIC chip 38  Silicon Chip – you can spot any logical errors in your program first. The second program is noppp.zip which, (when unzipped) contains the software which controls your computer’s parallel port and sends the programming data to the PIC. It’s available from the Oatley Electronics website, or from Michael Covington's website, www.mindspring.com/~coving-ton.noppp (links also available from www.siliconchip.com. au). Demo.asm Let’s look briefly at that chaser program assembly language code. Note the notes: throughout the listing there are notes, or comments, (each line or part of a line commencing with a semicolon [;]). These have no effect on the program (the assembler will ignore them) but remind the programmer later on what, or why, parts of the program achieved. They’re like a “rem” statement in BASIC and other programs. The first few lines are such comments. The first “real” instructions are the lines which begin: processor 16f84 (tells the assembler to use the instruction set for the 16F84 PIC); include <p16f84.inc> (says to include a set of predefined constants in a file called P16F84.INC; and _config RC _OSC & _WDT_OFF & PWRTE_ON (sets various configuration bits in the PIC to turn some hardware features on and off – the RC oscillator on, the “watchdog” timer off and the automatic power-up reset timer on. It is important to use the _config instruction in any programs used with this PIC Programmer. The assembler program will not be doing the actual programming, only creating a file with the numbers that will be transferred to the PIC chip as a second step. The two equ instructions reserve memory space in the PIC’s RAM for two variables called J and K at hex 1E and 1F. Counters are stored here to keep track of how many times a loop has been repeated. This is similar to declaring variables in BASIC but we need to tell the PIC which RAM locations will be used. The org instruction tells the assem- Fig.4: MPLAB, a free (but lengthy) download from www.microchip.com, allows you to assemble and test PIC programs before committing them to the chip. Not only does that save you time, it also saves you wearing out the PIC chip (you only have 1000 or so erase/program cycles to play with!) Parts List 1 PC board, 107 x 60mm 1 DB25 male socket, PCB mounting 1 18-pin IC socket 1 plugpack supply, 13.8VDC (nominal) <at> 1A (around 1718VDC no load) Semiconductors 1 PIC16F84, PIC16C84 or PIC16F83 microcontroller (unprogrammed) 1 BC548 NPN transistor 2 1N914 signal diodes 2 LM317 adjustable positive regulators Fig.5: one of the screens from Michael Covington's “NOPPP” PIC programming software. The first screens allow you set your printer port and the type of PIC. After inserting the PIC and turning power on, you are presented with the programming options (shown) from which you can load the HEX file compiled by MPLAB, change the type of PIC, program a PIC, erase a previously programmed PIC and verify that the PIC has been programmed correctly. bler that the program starts at location 0 in program memory and that the actual program is next. The follows a comment (;Program) and the first of the real PIC instructions: movlw B’00000000' clears a working register called W. That number is coped into the TRIS control register for port B (tris PORTB), setting pins 6-13 to output pins instead of input pins. Next, the program puts a binary 1 into the W register (movlw B’00000001') and copies it to port B, (movwf PORTB) which lights the LED connected to pin 6. Almost immediately, though, the program executes a RIF command which rotates the contents of port B to the left, changing the data to 00000010. Because the processor works so fast, you wouldn’t actually see the “chase”, so a delay loop is built in before the data shifts and the next LED lights. This stores the decimal number 50 in locations J & K then uses the decfsz instruction to count down from 50 to 0. This gives a delay of about half a second, after which time the goto mloop instruction repeats the process. The next LED (on pin 7) is lit and the LED on pin 6 is extinguished. The data then changes to 00000100, then 00001000, and so on, lighting each LED in turn after the delay loop. The end control is not a CPU instruction; rather it tells the assembler that the program is over. Compiling the program Having typed, or downloaded the assembly language program, now we come to compile it using the Microchip MPLAB program. MPLAB comes with ample instructions so we won’t go into it in depth here. As downloaded, MPLAB is zipped so must be unzipped and installed. Then it is opened in Windows. Just one point, though: when compiling demo.asm, MPLAB will give you an error message because the TRIS instruction previously mentioned has been discontinued by Microchip. As we have used it, though, it still works fine on the PIC chips described. TRIS should not be used on “real” applications, as distinct from this demo program. (There are other ways to do the same task but they are not as simple). PIC “Burning” This is where the second program, noppp.zip, comes in. Again, as downloaded, it is zipped. This program, though, operates under DOS or Windows 95/98/3.11. If you’re still using Windows 3.11 (unlikely, if you’re into programming PICs!), it’s better to use full screen mode rather than a window. Capacitors 2 10µF 25VW PC electrolytics 2 1µF 25VW PC electrolytics 3 0.1µF monolithic bypass capacitors Resistors 1 4.7kΩ 1 2.2kΩ 1 1.2kΩ 3 1kΩ 1 270Ω 2 120Ω 1 200Ω horizontal trimmer Extra components required for demonstration “Chaser” 1 programmed PIC16F84 8 LEDs, same colour 8 390Ω resistors 1 10kΩ resistor 1 0.1µF polyester or monolithic capacitor 1 .01µF monolithic capacitor 1 18-pin IC socket It was written to run under DOS to provide the clock pulses necessary for programming. You will recall these pulses need to be at least 0.1µs long. In practice, they are made longer to avoid any signal “bounce” in the cables. But they cannot be too long, or programming will be slowed down too much. Because of the huge range of computer speeds now available, it was also important that the timing pulses not depend on the CPU speed. This has been done using one of the timers built into the PC motherboard. One of these timers, the one normally used to produce tones from the internal speaker, can be set to provide a delay of 25µs. So even on the fastest Pentiums the programming pulses are not too short. By the way, the software will even work on a 4.77MHz XT! A screen grab of the NOPPP program is shown in Fig.5. As you can see, it is MARCH 1999  39 a simple menu-driven program which gives you a number of self-explanatory options. Before you get this far, however, you should have connected the programmer to the parallel port without power connected to the programmer. In fact, you should NEVER connect the programmer with power on, nor should you insert or remove a PIC chip from the programmer with power on. The PIC chip should be in place before plugging the programmer into the parallel port. In general, you would load an object-code file (with .hex extension) into memory, select the type of PIC to be programmed, apply power to the programming board and program the PIC. You should always verify that the program has transferred to the PIC before exiting the program, turning power off to the programmer and removing the PIC chip. Obviously, the same menu is used to erase an existing program in a PIC. Variable 5V supply Earlier, we mentioned that the 5V supply can be varied between +4V and +6V. This is used in the verify process to ensure that the PIC has indeed been programmed correctly and guarantees reliability. By far the greatest unreliability in EPROMs is caused by some cells not being completely erased before being re-used, or not being completely programmed. If a particular location is only partly programmed it might read correctly for a while but then shift to a wrong value with age or changes to the sup- info.com ply voltage. By programming the PIC with a 5V supply, then verifying it at 4V, 5V and 6V, you change the threshold voltages that define the 0s and 1s and so any marginally programmed bits will change with the changed supply voltage. It’s a double check that even many high-priced commercial programmers don’t have available. But with this cheap and easy to use programmer, once you have fully verified your PIC is programmed, you know it really is! Exact voltages aren't important – simply program with the trimmer at its centre position (5V), then verify with the trimmer at its centre, minimum (4V) and maximum (6V). Each instruction is a 14-bit word divided into an OPCODE which specifies the instruction type and one or more operands which further specify the operation of the instruction. The instruction set summary lists byte-oriented, bit-oriented, and literal and control operations. Opcode field descriptions are shown below. For byte-oriented instructions, ‘f’ represents a file register designator and ‘d’ represents a destination Where do you get it? The complete kit of parts –  PC board, components to build both the PIC Programmer and the demo chaser – is available by mail order from Oatley Electronics for $29.00 plus $6.00 pack & post. (PO Box 89, Oatley NSW 2223, phone (02) 9584 3563, fax (02) 9584 3561, email oatley<at>world.net or via website www.oatleyelectronics. com.au). A 13.8V/1A (nominal) plugpack power supply (which actually puts out about 17V or so) is available for $12.00, while additional PIC16F84 chips are also available for $12.00. *Michael Covington's own website (see below) is regularly updated with latest versions of software, etc and is a good site to visit for a mine of information if you're at all interested in PICs or PIC SC programming. Here's where to find the file downloads or links to downloads mentioned in this article. * In general, ftp sites are better for larger files Filename/Size Details Downloadable from NOPPP(1).ZIP Zipped file containing 169KB noppp.exe, noppp.c nopppf4s.tif, demo.asm, demo.hex, readme.txt & topic02.zip www.mindspring.com/~covington/noppp www.siliconchip.com.au www.oatleyelectronics.com.au MPL40(1).ZIP Zipped file containing 8.32MB MPLAB software http://www.microchip.com ftp://ftp.microchip.com * 51025b.pdf 3.12MB Adobe PDF file containing full MPLAB manual http://www.microchip.com ftp://ftp.microchip.com * 30430c.pdf 1.35MB Adobe PDF file containing full PIC 16F8X application notes http://www.microchip.com ftp://ftp.microchip.com * 40  Silicon Chip PIC 16XFX INST OPCODE FIELD DESCRIPTIONS f W b Register file address (0x00 to 0x7F) Working register (accumulator) Bit address within an 8-bit file register k Literal field, constant data or label x Don’t care location (= 0 or 1) The assembler will generate code with x = 0. It is the recommended form of use for compatibility with all Microchip software tools. d Destination select; d = 0: store result in W, d = 1: store result in file register f. Default is d = 1 label Label name TOS Top of Stack PC Program Counter PCLATH Program Counter High Latch GIE Global Interrupt Enable bit WDT Watchdog Timer/Counter TO Time-out bit PD Power-down bit dest Destination either the W register or the specified register file location [] Options () Contents → Assigned to <> Register bit field ∈ In the set of italics User defined term (font is courier) Note 1: When an I/O register is modified as a function of itself ( e.g., MOVF PORTB, 1), the value used will be that value present on the pins themselves. For example, if the data latch is ‘1’ for a pin configured as input and is driven low by an external device, the data will be written back with a ‘0’. 2: If this instruction is executed on the TMR0 register (and, where applicable, d = 1), the prescaler will be cleared if assigned to the Timer0 Module. 3: If Program Counter (PC) is modified or a conditional test is true, the instruction requires two cycles. The second cycle is executed as a NOP. TRUCTION SET designator. The file register designator specifies which file register is to be used by the instruction. The destination designator specifies where the result of the operation is to be placed. If ‘d’ is zero, the result is placed in the W register. If ‘d’ is one, the result is placed in the file register specified in the instruction. For bit-oriented instructions, ‘b’ represents a bit field designator which selects the number of the bit affected by the operation, while ‘f’ represents the number of the file in which the bit is located. For literal and control operations, ‘k’ represents an eight or eleven bit constant or literal value. The instruction set is highly orthogonal and is grouped into three basic categories: Byte-oriented operations Bit-oriented operations Literal and control operations All instructions are executed within one single instruction cycle, unless a conditional test is true or the program counter is changed as a result of an instruction. In this case, the execution takes two instruction cycles with the second cycle executed as a NOP. One instruction cycle consists of four oscillator periods. Thus, for an oscillator frequency of 4MHz, the normal instruction execution time is 1µs. If a conditional test is true or the program counter is changed as a result of an instruction, the instruction execution time is 2µs. MARCH 1999  41