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Got a concept you’d like to try before building a full prototype? New to microcontrollers but want to learn more about them? This combined PIC programmer and test bed could be just what you’ve been looking for. PIC TestBed Easy PIC programming and prototyping. Design by Barry Hubble Article by Peter Smith    Please note: The PicProg software described in this article is outdated and will not work on recent model PCs. A suitable alternative is WinPIC, which can be obtained from http://people.freenet.de/dl4yhf/winpicpr. html. Before use, configure WinPIC to use an interface type of “COM84 programmer for serial port” and select the correct COM port from the drop-down list. These settings can be found on the “Interface” tab. LO RES TO BE REPLACED I f you’re a regular reader of Silicon Chip, you’ll have noticed more and more microcontroller-based projects appearing in our pages – especially those using PIC microcontrollers. 76  Silicon Chip These little devices are extremely versatile, allowing much more functionality to be packed into less space than is possible with traditional components. Just as importantly, they’re cheap and easy to obtain, and are well supported with a wealth of free development tools and example applications. Back in the March 1999 issue, we described a simple PIC programmer all? One reason might be to really slow PIC can sink and source up to 25mA at that has proved very popular. Although down the action so that you can “see” its port pins (PICs rule, OK?). it includes a LED chaser circuit that what is happening on the PIC’s I/O To accommodate the two popular can be used to demonstrate PIC opport pins. This could be very handy LCD hardware interfaces, the PC board eration, it really is little more than a for tracking down elusive bugs or even has been designed to allow installation programmer. for learning PIC basics. of single or dual row headers (CON3 This new design integrates a proTo ensure orderly startup each time and CON4). The pinouts are compatigrammer with support for several power is applied, the PIC includes ble with the “Hitachi” standard as used popular I/O (input/ on virtually all alphanumeric LCD output) devices, along modules. Trimpot with header pins givVR3 provides disFeatures ing access to each Supports PIC16C84, PIC play contrast (also 16F84 and PIC16F84A mic rocontrollers individual port pin. Simple programming via called viewing anWindows-based software Space prevents gle) adjustment. ZIF (zero insertion force) socket provides easy PIC us from describing Note that no provichip insertion & removal Clock source can be crysta PIC microcontrollers l, resonator or variable RC sion has been made oscillator Header pins allow easy acc in detail, so we’ve ess to all port lines for connecting LCD Basic serial (RS232) inte assumed that you back-lighting, as this rface included have at least a baLCD module support tends to vary consic knowledge of siderably between 8 LEDs for PIC outputs (RB 0-RB7), jumper selectabl the subject. If we e manufacturers. Variable voltage on RA0 (fo r PICs with A-D inputs) lose you, don’t be RA0 (pin 17) and Push button input on RA disillusioned; vast 1 RA1 (pin 18) of the Reset button quantities of (free) PIC have been nomiinformation for exnated as receive (RX) perts and beginners and transmit (TX) alike is available on the Internet (see internal reset circuitry. Our circuit data for the serial inlink list below). If you prefer hardcopy, adds an external RC network and terface. Alternatively, the larger technical bookshops can pushbutton switch (S2) so that you these pins can be configured as variable often help, too. can reset the chip without having to voltage and momentary switch inputs, You might also like to review the remove power each time you want to depending on the positions of JP13 Silicon Chip March 1999 PIC Prorestart your program. Diode D2 isolates and JP14. grammer project, which describes the the reset circuit from the programming Whoa, what’s the variable voltage PIC16F84 in a little more detail. This interface but more on that shortly. input for? Let’s just say that it can be issue is still available – see page 75 for used for other 18-pin PICs, such as the ordering details. Input and output devices PIC16C71X series, which include onA whole string of jumper pins on board A-D converters. The programCircuit description the board allows selection of one of ming software doesn’t support these For ease of description, let’s break two functions for most of the PIC’s devices, however. the PIC TestBed circuit into three secinput/output pins. In addition, the Connection to the serial interface tions, as follows: jumper pins can be used to gain easy is made via an on-board 9-pin ‘D’ 1) Life support (power, reset and access to the port lines for connection connector (CON2). We’ve called it a   oscillator) to prototyping circuits, etc. Jumper “simple” serial interface because it 2) Input and output devices wires for this purpose can be fashioned doesn’t support hardware handshak3) Programming interface from matrix pin sockets, heat-shrink ing. RTS/CTS (pins 7 & 8) and DSR/ tubing and light-gauge hookup wire. DTR (pins 6 & 4) are simply looped Life support Alternatively, you can purchase the back to signal an “always ready” conReferring to Fig.1, you can see that ready-made Basic Stamp jumper kit dition. Conversion between the +12V a typical 3-terminal regulator (REG1) from Dick Smith Electronics (Cat and -12V levels on the RS232 lines and together with a sprinkling of filtering K-1406) or MicroZed Computers. the PIC (which works on 0-5V levels) capacitors and a polarity protection Port pins RB0 - RB7 can be indiis achieved with IC1, a MAX232. The diode (D1) provides 5V power to the vidually jumpered to drive the LEDs MAX232 includes an on-chip charge circuit. (LED1 - LED8) or in conjunction with pump voltage converter to boost the PICs have an internal clock oscilpins RA2 - RA4, an LCD (Liquid Crystal +5V supply to the higher RS232 levels, lator that requires only an external Display) module. Note, however, that eliminating the need for separate +12V crystal, resonator or RC network. All it is possible to have both the ‘a’ and and -12V supplies. three of these options are provided for ‘b’ jumpers installed together, as the on the Test Bed, with JP12 selecting Programming interface PIC can drive both the LEDs and LCD between the crystal/resonator and the without problems. The most important feature of the RC network. Trimmer pot VR2 allows As you can see, the LEDs are conPIC programmer we described in the you to quickly tune the RC network to nected directly to the PIC’s port pins Silicon Chip March 1999 issue was its the desired frequency. (via jumpers JP4 - JP11) without drivers simplicity. In fact, the designer calls Why bother with an RC network at or buffers. This is possible because the it the “No Parts PIC Programmer”. Of · · · · · · · · · · · January 2001  77 78  Silicon Chip Fig.1: the PIC programmer and test bed. It’s easy to build and just as easy to use! LO RES TO BE REPLACED Fig.2: follow this component overlay as an aid in assembly. The order is given in the text. course, it does have a few components. In fact, it has more than this design! First up, we should mention that PICs are programmed in a serial data format, requiring only two signal lines and a programming voltage. To enter programming mode, the MCLR pin is raised to 12-14V. Data to be programmed is then presented in a serial stream (one bit at a time) on RB7 and clocked in with pulses on RB6. The data format and timing used is of course important and is described in detail in Microchip’s “In-Circuit Serial Programmers Guide”. Microchip calls this programming method “ICSP”. All this means is that PICs can easily be programmed (or reprogrammed) while they are plugged in to the end product. On the PIC Test Bed, the MCLR, RB6 and RB7 pins are routed to a 5-pin header (CON5). In programming mode, these become the VPP, CLK and DATA signals, respectively. 5V (VDD) and GND (VSS) are also made available on the header. A number of commercial programming adapters are available that will plug directly into this header. This not-quite-same-size pic (no pun intended!) can be used in conjunction with the component overlay above when constructing the PIC TestBed. Fig. 3, the artwork for the board label which can be photocopied and glued to the board, as seen above. January 2001  79 Parts List: PIC Test Bed 1 PC board, code 07101011, 124 x 172mm 1 SPST PC-mount pushbutton switch 1 SPST tactile switch 1 2.5mm PC mount DC socket 1 9-pin female right angle PC mount ‘D’ connector 2 40-way dual row 2.54mm headers 1 40-way single row 2.54mm header 1 40-way header socket (Altronics cat P-5390 or sim.) 1 single row machine pin socket strip (6-way or larger) 24 jumper shunts 1 16-pin IC socket 1 18-pin ZIF (zero insertion force) IC socket 1 9V or 12V DC 300mA plugpack Semiconductors 1 MAX232A RS232 driver/receiver (IC1) 1 PIC16F84, PIC16F84A microcontroller (IC2) 1 78L05 5V regulator (REG1) 9 5mm red LEDs (LED 1 - LED9) 1 1N4001, 1N4004 1A diode (D1) 1 1N5819 Schottky diode (Altronics Cat Z-0040) (D2) 1 4MHz parallel resonant crystal (X1) Resistors (0.25W 1%) 1 100kΩ 3 4.7kΩ 1 470Ω 9 390Ω 1 100kΩ miniature horizontal trimpot (VR2) 1 10kΩ miniature horizontal trimpot (VR3) 1 5kΩ miniature horizontal trimpot (VR1) Capacitors 1 470µF 25V PC electrolytic 1 10µF 16V PC electrolytic 1 0.47µF monolithic ceramic 8 0.1µF monolithic ceramic 2 15pF ceramic But we’ve got an easier way! A tiny adapter board containing just a header plug and three resistors are all that we need (see Fig.4). The adapter board also provides termination for a serial cable that connects to your PCs serial port. How does such a simple scheme work? Well, the 12V signal levels on the RS232 interface are just what we need for the programming voltage. But what about the CLK and DATA signals, which should only be 5V maximum? The PIC clamps its port pins internally and with the aid of the 4.7kΩ resistors, current flowing into the pins in limited to a safe level. The Microchip people would surely frown on this method of programming their chips but we’re assured that in practice it works just fine (at least, in a hobbyist situation). A word of warning, though. Some serial ports, such as many found on older model laptops, do not generate true RS232 voltage levels. Signal levels may only reach between about 5V to 10V, which is clearly too low for the PIC programming voltage. The remainder of the magic is performed by Windows-based software, which reads your assembled PIC program code and drives the serial port lines in the necessary sequence to perform the programming. By the way, you will need to remove jumpers from JP10 and JP11 before connecting the programming adapter so as not to overload the signal lines. This also prevents potential damage to the LCD from the higher voltage levels present. Assembling the board Begin by checking the board for defects, in particular around CON3 where the tracks and pads are quite tightly Additional parts for programming adapter 1 PC board, code 07101012, 20 x 45mm (optional, see text) 1 9-pin or 25-pin female ‘D’ connector 5-core data cable, length as required 1 small cable tie Heatshrink tubing Additional parts for LCD (optional) 1 alphanumeric LCD module 150mm 14-way rainbow or IDC ribbon cable (see text) 2 14-way IDC sockets (Altronics Cat P-5314) (see text) Fig.4: here’s the circuit for the programming adaptor which can be built on the PC board as illustrated below (Fig. 5), or even as part of the cable (as shown overleaf). Misc. 200mm 0.71mm tinned copper wire 6 4G x 12mm wood screws or self tappers 1 190mm x 140mm wooden photo frame 4 small stick-on rubber feet Where to get the parts The only part that could present a problem is the 18-pin ZIF socket. We found a source at Futurlec (www.futurlec. com). A good selection of PIC chips, crystals and resonators can be found at MicroZed Computers. Jaycar, Dick Smith Electronics and Altronics also list a few types of PICs as well as LCD modules. 80  Silicon Chip Fig.5: the component overlay for the programming adaptor. Fig.6: samesize artwork for the adaptor PC board. Table 1: Useful PIC Resources On The Internet www.microchip.com The PIC manufacturers. Check here first! www.geocities.com/SiliconValley/Way/5807 Very comprehensive PIC resource list. home.iae.nl/users/pouweha/index.shtml How to control an LCD (the source of the LCD code in TESTBED.ASM) www.microzed.com.au Commercial site (Australian) www.dontronics.com Commercial site (Australian) spaced. Using Fig.2 as a guide, install the five wire links, followed by the resistors, diodes and capacitors. Note that capacitor C1 forms part of the RC oscillator and can be socketed for easy replacement. On the prototype, we snapped off a 3-pin section of a machined-pin socket strip for the job, then cut off the bottom of the middle pin. The crystal (X1) can also be socketed in the same manner. If you intend using a ceramic resonator rather than a crystal, you will note that there is no connection for the middle (ground) pin of the three-legged variety. No problems were found using resonators up to 10MHz without the ground connection. The socket for IC1 can be installed next, but don’t plug in the MAX232 chip just yet. Follow this with all LEDs, trimmer pots, switches and the 3-terminal regulator (REG1). All the jumper pin sets, as well as the LCD and ICSP connectors need to be made by cutting sections from the longer header strips shown in the parts list. The jumper pins (JP1 - JP14), as well as the pins marked “GND” (next to JP14), are made by cutting off two pairs of pins for each jumper pair. For the LCD interface, either CON3 (dual row header) or CON4 (single row header) can be installed, depending on which type of connector your LCD module supports. To hook up the LCD, a short length of ribbon cable (no more than about 150mm) is required. For single-row connector styles, you can make up the cable using a length of rainbow cable and two 14-pin header sockets. Once again, these are cut down from the 40-pin length shown in the parts list. For dual-row connector styles, use IDC ribbon cable and IDC sockets instead. Observe antistatic precautions when handling LCDs as they are particularly static sensitive. Install the ZIF socket (IC2) as the final step. Before plugging in IC1, apply power and use a multimeter to check that the 5V supply rail is OK. A good place to do this is between pin 15 (GND) and pin 16 (VCC) of the IC1 socket. The parts list specifies a MAX232A Fig.7: same-size artwork for the PC board, as viewed from the copper (ie, non-component) side. January 2001  81 Table 2: Some Of The Relevant Literature Available From Microchip Document No. DS30262C DS30277C DS35007A DS51025D AN555 AN587 Description PIC16F8XX EEPROM Memory Programming Specification In-Circuit Serial Programming Guide PIC16F84A Data Sheet MPLAB IDE, Simulator, Editor User’s Guide (includes tutorial) Software Implementation of Asynchronous Serial I/O Interfacing to an LCD Module for IC1. The ‘A’ at the end essentially means that the four charge pump capacitors (C2-C5) can be as small as 0.1µF, whereas on the non-‘A’ version, they are usually about 10µF. However, the non-‘A’ version works fine with 0.1µF capacitors up to around 64kb/s. also try TESTBED.ASM, which combines the LED chaser with an LCD test. It also provides an excellent example of how to program LCDs. So far we’ve only mentioned the .ASM, or assembly language versions of these programs, which must first be assembled into machine code before they can be programmed into a PIC. Despair not, we’ve also included the assembled versions (DEMO.HEX and TESTBED.HEX), all ready to be “burnt”. Which leads us to the programming software. A freeware program called PicProg handles the programming side of things (see Figs.9 and 10). PicProg runs on Windows 3.x and Windows 95/98, on any hardware with a 486DX processor and above. There are no special installation requirements; simply unzip PICPRG06. ZIP into your folder of choice, and set up a shortcut to the PICPROG.EXE file. By the way, all of the software mentioned (with the exception of MPLAB) The programming adapter The only parts needed for the programming adapter are three 4.7kΩ resistors, a length of 5-core cable, a 9-pin (or 25-pin) female ‘D’ connector and a 5-pin header socket. If you wish, you can use a PC board to mount the resistors and the header socket and to terminate one end of the cable. Alternatively, you can dispense with the PC board altogether and solder the resistors “in-line” with the header socket and cable. Figures 5 and 8 show how to construct the adapter using either method. As shown in our photos, we used a rather unconventional method to “house” the prototype; a wooden photo frame fitted with rubber feet! If you don’t like this idea, you could use plastic stand-offs or even large rubber feet. It’s a good idea to label the jumper pins, too. We’ve included a simple label (Fig.3) that you can photocopy and stick on. Software The software of choice for PIC program development is MPLAB, a complete collection of all the tools you need to edit, assemble and debug PIC code. Best of all, it is available free of charge from Microchip, on the web at www.microchip.com If you don’t have a lot of PIC programming experience, you might like to use the little programs we’ve adapted for testing the completed board. First of all, there’s DEMO.ASM, a simple LED chaser that will check out the 8 LEDs. If you’ve connected an LCD, you can 82  Silicon Chip Fig.8: alternative programming adaptor, with no PC board required. Be sure to insulate all components! Experienced PICers Read This! PicProg was developed as a 16C84 programmer. There are a number of small but important differences between the 16C84 and the newer 16F84 and 16F84A PICs that need to be considered. The most obvious differences exist in the Configuration word. The polarity of the PWRTE bit is inverted in the F84/F84A, so selecting this fuse in PicProg (ticking the “PWRTE” box) when programming a F84/F84A causes the Power-up Timer to be disabled. Bits 4-13 of the Configuration word are designated as Code Protection bits in the F84/F84A. However, on the C84, only bit 4 is significant. We’re unsure how PicProg handles undefined bits, so selecting the Code Protect fuse may not result in protection. You can, of course, perform a read after programming; if the resultant data is invalid (all zeros, for example) then code protection is working. We were able to successfully code protect our test PICs. The different Configuration word masking also means that PicProgs checksum computation will be incorrect on both the F84 and F84A. Most would consider this insignificant. The author has no intention of updating PicProg to specifically support the F84/F84A. However, we are aware of a second freeware programmer, called ICProg, which does support the newer PICs and is compatible with the TestBed. We were amazed by the enormous range of options provided by ICProg, but in use found that it was unable to successfully program EEPROM data memory in a PIC16F84A (we tried version 1.03A). If this problem is ironed out, ICProg could be well work a look. Check it out at www.h2deetoo. demon.nl ’Nuff said. Our tests convinced us that PicProg effectively programs both types of chips! Fig.9: the main programming screen: you should see this when you run the PicProg.exe program. As you can see, all parameters are set from this screen . . . is downloadable from the SILICON CHIP website, www.siliconchip.com.au After launching PicProg, select Setup from the main menu and choose which serial port you’ve connected to the TestBed (see Fig.10). Next, load the code (.HEX) file that you want to burn, then select the appropriate Fuse options. These are fully explained in . . . except the port parameters which are shown on this screen (fig. 10). It gives you the option of changing the port – and it also remembers which port you’ve set next time around. the PIC data sheets (hint: select “XT” if you’re using a 4MHz crystal). Finally, hit the Program Chip button, and if all goes well, programming will complete in a matter of seconds! PicProgs on-line help includes a couple of useful tips, so check these out if you get stuck. Note that the Test Bed programmer is compatible with the “LudiPipo” programmer mentioned throughout the PicProg documentation. All credits for PicProg go to Tord Andersson, who has been kind enough to make his software available to all for non-commercial use. Well, that’s about it for this project. SC Happy PICing! 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