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The adapter can program virtually any Atmel microcontroller in-circuit. It’s shown here ready to program the microcontroller in the “IR Remote Receiver & Display” unit described last month. In-System Programming Adapter for Atmel AVR Microcontrollers If you’re interested in experimenting with microcontrollers but aren’t keen on spending big dollars on a “starter” kit, then this project is just what you’ve been looking for. Together with a Windows-based PC and some free software, it will allow you to program most Atmel AVR microcontrollers right in-circuit! I By PETER SMITH F YOU BUILT the “IR Remote Receiver & Display” described last month, this project will allow you to program the microcontroller chip yourself. In fact, that’s why we developed this simple circuit but it can also be used for programming almost any Atmel AVR microcontroller in-circuit. Basically, the device is a simple 68  Silicon Chip adapter that sits between the parallel port of your PC and the device to be programmed. It’s alive! If you’re new to microcontrollers, you’re probably wondering what all the fuss is about. Why do they need to be “programmed”? Microcontrollers are essentially microcomputers with built-in program memory, as well as other useful interface logic. When you buy one of these little devices from your local electronics outlet, its memory is blank. That is to say, it has no instructions “telling” it what to do. Before it can be used in project “X”, its memory must be programmed before it will perform as the project designer intended. So grab your blank micro and let’s head off to the lab for a memory implant … In days of old… Once upon a time, end-user-programmable microcontroller memory was EPROM-based. Like the traditional UV-erasable EPROM memory most readers would be familiar with, it’s programmed in a parallel fashion (one byte at a time) using high voltages. www.siliconchip.com.au But that’s all in the past. Flash memory technology now allows fast electrical erasing and programming at normal chip supply voltage levels. Add to that a “smart” serial interface and programming the current crop of microcontrollers becomes an almost trivial task. Atmel’s Solution Atmel microcontrollers incorporate a serial programming interface (SPI) that is designed specifically for in-system programming (ISP). Three I/O port pins do double-duty as control and data pins for the SPI. These are the serial input (MOSI), serial output (MISO), and serial clock (SCK) pins. Programming is achieved by holding the reset (RST) pin low continuously from power-on, then sending the appropriate commands and data to the serial input (MOSI) pin. Memory contents can be read out via the serial output (MISO) pin, which also provides status information. Data is shifted in and out of the SPI under control of the serial clock (SCK) pin. +5V VDD CRYSTAL OR OTHER CLOCK SOURCE 3 x 1k PB7/SCK XTAL1 PB5 PB5/MOSI XTAL2 PB7 PB6 PB6/MISO TO USER CIRCUITS SCK RES MISO ATMEL AVR MICRO MOSI RST GND +5V FROM RESET CIRCUIT A K OPTIONAL PROGRAMMING INDICATOR  1k TO ISP HEADER LED Fig.1: building in support for in-system programming in your designs is not difficult. In many cases, all that’s required are three additional resistors, as shown here. Connecting to the interface In order to program one of these micros, we need to connect some kind of programming adapter to the SPI pins. On the AT90S2313 microcontroller (as used in our IR Remote Receiver & Display project), the SPI signals appear on the same pins as the upper Port B input/output (I/O) signals – PB5, PB6 & PB7. These pins behave like any other port pins during normal operation but take on the SPI functions when programming mode is entered. In a typical design, external (user) circuits will be connected to some or all of the port pins. How do we prevent the obvious conflict that will occur between the user circuits and the SPI Fig.3: the pinouts recommended by Atmel for the serial programming interface. The header is of the standard 10-pin dual row variety. www.siliconchip.com.au Fig.2: designs that need more drive from the micro’s port pins may need a means of switching between the user circuits and programming interface. Here we show how this can be achieved using an analog multiplexer – an idea suggested by Atmel. signals? One possible solution is to build in isolation resistors, as shown in the simplified circuit of Fig.1. This works well if the I/O pins are used for inputs only, or if used for outputs, only need to sink or source a few mA of current. A universal solution is shown in Fig.2, where the user circuits are isolated with an analog multiplexer when in programming mode (RST signal low). Of course, the simplest solution of all would be to incorporate jumpers or DIP switches in the design so that Fig.4: a block diagram of the complete programming system. Power for the adapter is supplied from the target board. October 2001  69 adapter (they call it a “dongle”) that plugs into the parallel port of your PC. In conjunction with Windows-based software, it allows programming of both the data (EEPROM) and program (FLASH) memory in most of their microcontrollers (see Fig.4). Atmel supply the programming dongle with some of their microcontroller development kits. We know you probably don’t want to buy the whole kit (!), so we’ve designed an equivalent adapter based on information freely available on the Internet. Our programming adapter Referring to the circuit diagram in Fig.5, you can see that all that is required is a buffer (IC1) and a handful of resistors to provide some signal conditioning and circuit protection. In fact, we’ve seen some circuits published that connect the parallel port lines directly to the microcontroller’s SPI pins. We don’t recommend that approach at all, as damage to your computer, or more likely your microcontroller, is entirely possible. IC1 incorporates two quad tristate buffers, with their outputs enabled under software control by logic “low” signals on pins 1 and 19. As you can see, some outputs have been parallelled to increase drive capability. This is especially important for the reset (RST) line, which may have a strong pull-up to +5V on the target board. Fuse F1 and diode D1 provide basic reverse-polarity protection. The idea here is that the diode shorts the +5V supply to ground and blows the fuse if you should inadvertently reverse the power connection to the board. Note that reversing the ISP cable won’t blow the fuse but it may damage IC1. This is much less likely to occur if you use polarised (shrouded) headers at both ends, as the header plugs are keyed to match and will only mate one way around. By the way, we placed the fuse in the ground return instead of the Fig.5: the circuit uses a single 74HC244 octal buffer (IC1a & IC1b) plus a handful of resistors. This provides signal conditioning and protects the microcontroller to be programmed and the PC’s parallel port. the user circuits can be completely disconnected from the port pins when the programming adapter is connected. Trouble is, it’s a real pain having to continually install and remove jumpers each time you want to program and test your code (and for me, that’s lots ‘a’ times!). You might have noticed that we haven’t provided any isolation at all in our IR Remote Receiver and Display project. Careful port pin assignments and a little hocus-pocus in the micro- controller’s code allowed us to keep the parts count low. To provide a connection point for the programming adapter, the SPI signals are routed to a standard 10pin dual row header, with pinouts as defined by Atmel (see Fig.3). The header also provides power to the programming adapter. Atmel’s programming adapter As luck would have it, Atmel has designed a simple programming Table 1: Resistor Colour Codes  No.   1   7   1   7 70  Silicon Chip Value 100kΩ 10kΩ 470Ω 220Ω 4-Band Code (1%) brown black yellow brown brown black orange brown yellow violet brown brown red red brown brown 5-Band Code (1%) brown black black orange brown brown black black red brown yellow violet black black brown red red black black brown www.siliconchip.com.au Fig.6: follow this parts layout to build the PC board. Make sure that IC1, LED1 & D1 are installed with the correct polarity. Fig.7: the full-size etching pattern for the PC board. Check your board against this pattern before installing any of the parts. power rail in an effort to avoid the potential meltdown that could occur under certain circumstances. If the PC doing the programming is also used to power the target board and the power supply is reversed, then +5V is connected directly to the ground return of the parallel port (can anyone smell something burning…?). You may be wondering why we’ve specified a 250mA fuse when a smaller current rating would seem to be more appropriate. Unfortunately, smaller fuses have significantly higher resistance and would introduce a lot more “ground noise” into the circuit. Construction All parts are mounted on a 70 x 70mm single-side PC board. Referring to the overlay diagram (Fig.6), begin by installing the six tinned copper wire links and all the resistors. Next, install diode D1, the socket for IC1, the two capacitors and the fuse clips for F1. The two connectors can be installed next. Make sure that pin 1 of CON2 is aligned as shown on the overlay diagram; when aligned correctly, the keyed side of the connector faces inwards (towards the centre of the board). Also of note is the mounting method for CON1, the D-25 connector. Some variants of these connectors have solder tails to secure them to the PC board, whereas others need to be secured with M3 screws and nuts. www.siliconchip.com.au There’s no need to install the board in a case – just attach stick-on rubber feet to the corners to stop it scratching your desktop. If you have the type that requires screws, then be sure to fit the screws and tighten them up before soldering any of the pins. To complete the assembly, install IC1 and LED1, noting that the shorter lead of LED1 is the cathode and must be orientated as shown. Housing To keep costs down, we haven’t specified a case for this project. Sim- ply stick a small self-adhesive rubber “foot” in each corner to protect your desk and prevent the board sliding around too easily. Cables If your PC sits on your desk, then you might find that you can plug the adapter directly into the parallel port connector. Alternatively, you can make up a suitable cable using one metre of 26-way IDC ribbon cable and two October 2001  71 Fig.8: the software selects LPT1 by default. If you have connected to a secondary port, select it here. cable-mount 25-way IDC connectors. Remember that you need to strip one conductor off the ribbon cable before attaching the connectors. You could also use shielded data cable and solder-type D-25 connectors for the job. These will be a little cheaper than the IDC versions, but will take a lot longer to assemble. We don’t rec- Parts List 1 PC board, code 07110011, 70mm x 70mm 1 90° PC mount 25-pin male ‘D’ connector (CON1) (Altronics cat P-3220) 1 10-pin dual row PC-mount header (shrouded or ‘boxed’ type) (CON 2) 2 10-pin IDC (cable mounting) header sockets 1 20-pin IC socket (machined pin type) 1 M205 250mA fast-blow fuse 2 M205 PC-mount fuse clips 1m 10 way IDC ribbon cable Semiconductors 1 74HC244 octal buffer (IC1) 1 3mm red LED (LED1) 1 1N4001 1A diode (D1) Capacitors 1 0.47µF 63V MKT polyester 1 220pF 63V MKT polyester Resistors (0.25W, 5%) 1 100kΩ 1 470Ω 7 10kΩ 7 220Ω Miscellaneous 4 small self-adhesive rubber feet 10cm (approx.) tinned copper wire for links Optional (see text) 1 25-pin IDC male ‘D’ connector 1 25-pin IDC female ‘D’ connector 1m 26-way IDC ribbon cable 72  Silicon Chip Fig.9: most AVR micros can be programmed. Choose your chip! ommend pre-made printer extension cables be used, as they are generally too long and may introduce reliability problems; keep the length down to no more than about one metre if possible. For the connection to the target board, make up a second cable using a short length (no more than one metre) of 10-way IDC cable and two 10-way cable-mount IDC plugs. Testing Without the parallel port cable connected or the fuse installed, connect the ISP cable between the programming adapter and the board that contains the microcontroller that you wish to program (the “target” board). Apply power to the target board and connect the positive lead of your multimeter to the cathode end of D1 and the negative lead to the righthand fuse clip (the clip closest to the ISP cable). Your meter should read +5V. If all is well, install IC1 and the fuse, hook up the parallel port cable and get ready to “burn” your first microcontroller! Power-up sequence We recommend that you connect both adapter cables before applying power to the target board and remove power before disconnecting. This prevents damage to IC1 and the microcontroller that could be caused by “hot plugging” power to the adapter. We’ve included current-limiting re- sistors on the adapter inputs to protect IC1 and your PC’s parallel port lines, so it’s not necessary to power off your PC when connecting or disconnecting the adapter. Even so, some readers have suggested to us that if you intend controlling home brew devices with your parallel port, it’s not a bad idea to purchase a parallel port expansion card. The idea is that if something goes wrong, you damage the add-on card and (probably) not your motherboard. We agree! Installing the software You need a PC running Windows 95 or 98 to use this software. It might also run on Windows Me but we haven’t tried it. Unfortunately, it doesn’t work reliably on Windows NT4 and the same probably goes for Windows 2000, no doubt because it was never intended for these platforms. If you haven’t already done so, download the Atmel AVR ISR software from the Atmel ftp site at ftp://www.atmel.com/pub/atmel/avr_ isp.zip*. If you intend programming the microcontroller in the IR Remote Receiver and Display project (as we’ll do in the following example), then you’ll also need to download the program files for this project from the Silicon Chip website at www. siliconchip.com.au Unzip all files in the avr_isp.zip archive into a temporary directory and then double-click on the setup.exe file to launch the installation. Follow the on-screen prompts to complete the installation. Setting up the software When you run the AVR ISP software, you will be presented with a large empty window. From the menu bar, click on Options and choose Change Printer Port. If your adapter is connected to LPT1, you should get a display like that shown in Fig.8. Change the port if nec- Fig.10: for convenience, all settings for the session can be saved in a project file. www.siliconchip.com.au essary, and check that you get a “Dongle Found” message. If not, there may be a problem with your adapter of parallel cable. Click on the OK button to close the dialog. Still on the menu bar, click on Project and select New Project. A dialog box appears with a list of all supported microcontrollers (Fig.9). Select the AT90S2313 and click on the OK button. Three separate windows then appear, with the Project Manager window in front (Fig.10). Enter a title for the project, as well as any comments you like. Next, click on the Program Memory window to bring it to the front. Displayed in this window, in hexadecimal notation, are all the bytes that will be written to the micro’s FLASH (program) memory. Notice how all the bytes have been automatically initialised to FF, the value of “blank” (erased) memory. Individual bytes can be edited directly in the memory windows but thankfully, we don’t need to do that! To load the code for the IR Remote Receiver and Display project, click on File on the main menu bar and choose Load. A dialog box opens prompting you to choose the file to load, so navigate to wherever you unzipped the files for the project and choose the IRRLCD.HEX file. Now click on the OK button, and a message will appear stating that the file was loaded successfully. For this project, we also need to program the data (EEPROM) memory. Click on the EEPROM Data Memory window to bring it to the front. Note that by default, these windows are cascaded, but can be moved around for easier access. Follow the same procedure as before, but this time load the IRRLCD. EEP file (Fig.11). Fig.11: after loading the program and data files, your screen should look something like this. message will be displayed. Otherwise, you’ll hear a “beep” when it’s finished and see a message flash up so quickly that you don’t have time to read it. This indicates success! Want more information? Burn baby, burn! OK – check that everything is hooked up and power is turned on. Again from the main menu, click on Program. A drop-down list appears, giving you the option of erasing, programming, or verifying the device (FLASH memory) or EEPROM memory (see Fig.12). You could perform each of these operations in turn but there is a quick­er way. Select Auto Program from the list to have all the steps performed automatically in sequence. If all is well, a small dialog box with a progress bar appears (see Fig.13). Should the Auto Program sequence fail for any reason, an appropriate error www.siliconchip.com.au Before closing AVR ISP, don’t forget to save your project. Click on Project and select Save As. Enter a name for the project, navigate to wherever you want to save it and click OK. Note that project files should be saved with a .AVR extension for easy identification later. Then next time you want to reprogram the same device, simply select Project, Open Project to open the project file, and all your settings, including the program and data files, will be instantly reloaded. Fig.12: functions can be executed individually, or in automatic sequence using Auto Program. If you want to change the way Auto Program works, check out the Auto Program Options selection. Fig.13: if you get this far, you’re just seconds away from a successful implant! All the technical details on serial programming are included in the data sheets for each microcontroller type. Go to www.atmel.com to download your copy. While you’re there, check out AVR Studio, a complete development environment for AVR micros – and it’s free! Many of our projects also use PIC microcontrollers from Microchip. Unfortunately, they cannot be programmed with this adapter. However, the PIC Test Bed described in our January 2001 issue includes a simple serial programming scheme. *NOTE: the Atmel AVR ISP software is no longer available. Use Ponyprog instead. This can be downloaded from http://www.lancos.com/prog.html ­— set it up for the "AVR ISP (STK200/300) SC parallel port interface". October 2001  73