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Upload your microcontroller code in seconds with this new, PC-serial-port-connected programmer design. AVR ISP Serial Programmer This project will allow you to erase and rewrite the program and data memory in your AVR micro in a flash – without even removing it from the application circuit. Design by STEPHEN DAVIES Words by PETER SMITH 72  Silicon Chip www.siliconchip.com.au B ack in the October 2001 issue of Silicon Chip, we described an AVR ISP programmer with similar capabilities to those detailed here. The original design connects to your PC’s parallel port, with just one low-cost IC providing buffering between the SPI interface and parallel port lines. The emphasis of the design was on ease of construction and low cost. This new design is slightly more complex but it provides a number of useful additional features. For a start, most PCs have a free serial port, whereas the parallel port may already be used for a printer or scanner. Serial port interfaced devices are generally much more robust, too; there are no issues with inserting and removing the connector with power applied, and cable length is relatively unimportant. Best of all, support for the AVR ISP Serial Programmer is already built right into AVR Studio. This means that you can assemble, debug and then program your AVR micro, all within the same application. By contrast, the October 2001 design needs a separate application to perform the programming part of the cycle. AVR Studio, by the way, is a complete set of PC-based development tools for use with Atmel’s AVR microcontroller family. It includes a project manager, source editor, assembler and simulator – and it’s free! Serial versus parallel programming A potentially confusing aspect of AVR programming involves the terms “serial” and “parallel”. Most AVR devices can be programmed using a low-voltage “serial” method or a high-voltage “parallel” method. With serial programming, the RESET pin is held low while data is exchanged over a 3-wire Serial Programming Interface (SPI). No special programming voltages are required; the microcontroller’s supply pin remains within its normal operating range (usually 2.7-6.0V). Conversely, with parallel programming, the microcontroller must be supplied with 5V whilst the RESET pin is driven to 12V. In addition, eight bits of data are transferred simultane- ously rather than the bit-by-bit transfer of the serial mode. In all, fourteen distinct signals are required in parallel programming mode, making it considerably more difficult to implement. In-system programming The advantage of the low-voltage serial programming method is that it allows in-system programming (ISP). In-system programming means just that. There’s no need to even remove the AVR micro from its socket in order to reload program and/or data memory. In many cases, all you need to do to make use of this feature in your designs is provide a connection point (the ISP header) for the programmer. The block diagram in Fig.1 shows how it all hangs together. Fig.2 shows how the ISP header would be hooked up in a typical design. The AVR micro shown in this example uses the same pins for both the SPI signals (MOSI, MISO and SCK) and the upper port B I/O signals - PB5, PB6 & PB7. During normal operation, these three pins behave like all the other port I/O lines. However, when RESET is held low, the alternate SPI Fig.1: the programmer connects between your PC and the target board. Power is provided by the target board, thus eliminating the need for a separate supply. www.siliconchip.com.au October 2002  73 Fig.2: most AVR micros can be programmed via a 3-wire Serial Programming Interface (SPI). It’s just a matter of wiring the SPI signals to a header for connection to our programmer. In some cases, you may also need to add three 1kΩ resistors, as shown here. function is selected and programming operations can commence. Notice the three 1kΩ resistors in Fig.2. They provide a measure of isolation between the user circuits and the SPI signals. This works well if the I/O pins are used for inputs only or when used for outputs, if they only need to sink or source a few mA of current. A universal solution is shown in Fig.3, where the user circuits are isolated with an analog multiplexer when in programming mode (RESET signal low). Of course, the simplest solution of all would be to incorporate jumpers or DIP switches in the design, so that the user circuits can be completely disconnected from the port pins when the programmer is connected. in-system programming. Fuse bits How it works At this point, you’re probably wondering why we need the parallel programming method at all. Serial programming does the job, with fewer signals and at a lower voltage, doesn’t it? Well, yes - almost. The fuse bits on most devices can only be programmed with the parallel method. Fuse bits are used to control several important microcontroller features. They can be thought of as non-volatile switches. When on, the respective feature is enabled and when off, it is disabled. Fuse-selectable features vary according to device, so check your micro’s data sheets for details. In most cases, the factory-programmed fuse settings are fine for general use, so this serial programmer is probably all you’ll ever need! By the way, all AVR devices, with the exception of the AT90S8534, ATTiny11 and ATTiny28, support As you can see from the circuit diagram in Fig.4, there really isn’t much to the hardware side of the AVR ISP Serial Programmer. Most of the hard work is done by IC2, an AVR microcontroller. The design incorporates two serial interfaces. One connects to your PC’s serial port and the other to the SPI port on the microcontroller to be programmed. Conceptually, the microcon-troller (IC2) can be thought of as an intelligent “bridge” between these two interfaces. As you’ve prob- 74  Silicon Chip ably guessed, this “bridge” is needed because PC serial ports and SPI ports are entirely incompatible. Data is sent and received over the PC serial port lines at RS232 voltage levels (up to +/-12V). Translation to standard TTL levels (0 – 5V) is performed by IC1, a MAX232. This device incorporates a charge pump voltage doubler and inverter for generation of the required positive and negative voltages, hence the need for the 1uF capacitors. Unlike the PC interface side, the Serial Programming Interface operates at TTL voltage levels (0 – 5V). The SPI consists of three signal lines, namely: MOSI (Master Out Slave In), Fig.3: an analog multiplexer can be used to completely isolate the user circuits during programming Table.1: Supported devices ATTiny12 ATTiny15 AT90S1200 AT90S2313 AT90S2323 AT90S2343 AT90S4414 AT90S4433 AT90S8515 AT90S8535 Atmega83 Atmega103 Atmega161 Atmega163 MISO (Master In Slave Out) and SCK (Serial Clock). The microcontroller (IC2) is considered the serial bus “master”. It controls the SCK line, sending serial data on MOSI and receiving data on MISO. It also controls the target micro’s RESET line, driving it low to activate SPI (programming) mode. Connection to the target board is made via a 6-pin single-row header (CON3) or a 10-pin dual-row header (CON2). Pinouts for both headers are shown in Fig.5. The 10-pin header is optional. We’ve included it in the design because it tends to be the most common type in use on AVR development boards. Low-voltage operation Power for the programmer is derived from the target board. As shown, the programmer is designed to operate from 4.5-5.5V. However, some microcon-troller variants can operate over a much wider voltage range. For example, the AT90S1200-4 and www.siliconchip.com.au +V C1 1F C2 1F R1 10k 2 6 16 Vcc C1+ Vq C1q C3 1F C2+ CON1 8,10 14 3 Tx 7 5 Rx 13 1 RS232 TO PC SERIAL PORT 2 7 8 T1out IC1 C2q MAX232 T1in T2out T2in R1in R1out R2in 20 1 V+ R2out 1 C4 1F RES 3 4 C5 1F 5 11 PB7 11 9 10 6 12 3 9 2 PD6 PD3 PB3 PD2 PB2 PD1/TxD SC PB1 PD0/RxD PB0 GND X2 4 6 2002 PB6 PD5 GND 15 JP1 IN: BOOTSTRAP PROGRAMMING OUT: NORMAL D1 1N5817 4 x 100 SCK 7 MISO 9 17 MOSI 1 RESET 5 C6 22pF 15 14 13 4,6 8,10 JP1 CON3 ISP 12 10 4MHz 2 RES 5 4 5 1 TO TARGET BOARD 3 C7 22pF AVR ISP SERIAL PROGRAMMER TO TARGET BOARD 3 X1 X1 CON2 ISP (OPTIONAL) VCC 2 A 18 19 IC2 PB5 AT90S1200 8 16 OR PD4 PB4 AT90S2313 7 K C9 10F 16VW Vcc RES 4 9 C8 100nF 6 1N5817 A K Fig.4: the complete circuit diagram for the programmer. IC2 drives the target micro’s SPI lines in response to commands and data received from the PC serial port. AT90S2313-4 are specified for 2.7 – 6.0V. Higher speed devices such as the AT90S1200-12 and AT90S2313-10 are specified for 4.0 – 6.0V only. If you’re likely to be using the programmer with designs powered from less than 4.5V, then several points need to be considered. Firstly, you’ll note that we haven’t specified a speed rating for IC2 in the parts list. Any speed device (-4, -10 or -12) will work OK in the programmer if the target board supplies between 4.5 and 5.5V. However, for low-voltage operation, you should choose the –4 (4MHz) part. In addition, you will need to replace IC1 with a MAX3232 (or equivalent) device, suitable for operation down to 2.9V. By the way, we’ve nominated 2.9V instead of 2.7V, as this is the minimum programming voltage shown in Fig.5: pinouts for the two ISP header variants. Use the same pin assignments for your designs. www.siliconchip.com.au the most recent Atmel errata sheets. Finally, you’ll need to replace D1 with a wire link. Although we’ve specified a Schottky diode here, even its 0.2V drop will be too high at these low voltage levels. D1 provides reverse polarity protection but is unnecessary if you use the specified header sockets and plugs. These are polarised (keyed) and therefore impossible to accidentally reverse. Having said all that, we believe that the programmer will probably func- tion right down to 2.9V even without the lower-voltage components. No guarantees though! Microcontroller choices This project is based on Atmel’s application note AVR910. Atmel’s original design calls for an AT90S1200 device for IC2. We’ve retained support for this device, and included the option of using an AT90S2313 as well. The latter device is a little more expensive, but we believe that some The PC board is a snug fit inside the case - so snug, in fact, we didn’t worry about any mounting screws. Your PC board might need some minor surgery on the corners (with a file) to ensure it fits past the case corner pillars. October 2002  75 Fig.6: the overlay diagram with full-size PC board pattern shown “ghosted” underneath. The two pads above CON2 are for temporary connection to an external 5V DC supply (needed only during bootstrap programming). a kit, then there is no need to install JP1. This 2-pin header and its associated jumper shunt are only required for bootstrap programming, which we’ll look at shortly. Cable assembly A minimum of two cables is required for a working setup, so we’ll describe them first. For connection to your PC’s serial port, you’ll need a length of 9-way IDC cable with a 9-pin male ‘D’ connector on one end and a 10-way header plug on the other. Cable length is not critical and can be up to 1.5m or more. Fig.7 shows the details. For connection to your target boards, a much shorter length of 6-core data cable or 6-way rainbow cable is required. We recommend a maximum length of about 250mm. Each end should be fitted with a 6-way header plug, wired pin to pin (see Fig.8). If you own one of the many development boards that use 10-way headers for the ISP connection, then you’ll want to make the optional 10-way cable. All that’s required is a 250mm length of 10-way IDC cable with an IDC header plug on either end. Bootstrap programming This photograph of the completed PC board is actually larger-than-life so you can clearly identify the components and their placement. enthusiasts will already have a spare one or two of these in their parts bin! The AT90S2313 is pin-compatible with the AT90S1200 but includes extra goodies such as SRAM, a UART and more program (Flash) memory. The designer has modified Atmel’s original program so that it will run on the AT90S2313 but a little more on that shortly. Construction Referring to the overlay diagram in Fig.6, begin by installing the three wire links. Next, install all of the resistors followed by diode D1. Be sure to align the cathode end of D1 (indicated by a white band) as shown. The remaining components can be installed in any order you wish but leave the crystal (X1) and the connectors (CON1 – CON3) until last. CON1 and CON3 (optional) should be aligned with pin 1, or the polarised side, facing towards the middle of the board. When soldering, make sure that the connectors are seated firmly against the PC board surface. 76  Silicon Chip The crystal (X1) is mounted in the vertical position. Once in place, use a length of tinned copper wire to attach the body to the ground pad underneath, shown marked with an asterisk (*) in Fig. 6. Note that if you have a pre-programmed microcontroller (IC2), as would be the case if you’ve purchased Fig.7: the RS232 cable is made up using two crimpstyle IDC connectors. Note that the header plug has one more pin than the ‘D’ connector does. This is easily handled by crimping the header plug first, then stripping back the 10th conductor and snipping it off where it enters the header. As with any other micro project, the program (Flash) memory in IC2 needs to be programmed before it will perform as designed. If you’ve purchased this project as a kit, then the micro will already be programmed. You should skip this section and go directly to “Housing”. However, if you’ve sourced all the bits individually, then Fig.8: connection from programmer to target board is via one of these ISP cables. www.siliconchip.com.au you’ll need to program IC2 yourself. The program files for IC2 are available from the Silicon Chip web site at www.siliconchip.com.au If you have an AT90S1200, then download the AVR910a.ZIP file. Alternatively, for an AT90S2313, download AVR910b. ZIP. Inside these .ZIP files you’ll find both the assembled (.HEX) file ready for upload to the micro as well as the source (.ASM) file. If you have access to another (working) ISP programmer, simply connect it to one of the ISP headers (CON2 or CON3), hook up an external 5V DC supply and you’re ready to upload the code. We’ve provided a convenient connection point for the external supply in the form of two spare pads, situated just above CON2. Refer to the overlay diagram (Fig.6) for details. Oh, and you’ll need to install a shorting link on JP2 during programming, too. Don’t have access to a working programmer? No problems – we’ve devised a method of “bootstrap programming” IC2 to cater for this very dilemma! You’ll need a free parallel port on your PC, a “bootstrap programming” cable, an external 5V DC <at> 50mA power source and Windows programming software. Let’s make the cable first. Using a 450mm length of data cable or rainbow cable, solder a 25-pin male ‘D’ connector to one end and a 6-way header socket to the other. Fig.9 shows the pin connections. For connection to an external power source, solder two lengths of hook-up wire to the spare pads situated just above CON2 (see Fig.6). Next, download and install the Windows programming software. The Parts List – AVR ISP Serial Programmer 1 PC board coded 07110021, 78.5mm x 49.5mm 1 82 x 54 x 31mm (L x W x H) plastic instrument case (Jaycar cat HB6015, Altronics H 0205) 1 4MHz crystal (HC49 package, parallel resonant) (X1) Semiconductors 1 MAX232 RS232 line driver/receiver (IC1) 1 AT90S1200 microcontroller (IC2) programmed with AVR410a.HEX –or1 AT90S2313 microcontroller (IC2) programmed with AVR410b.HEX (see text) 1 1N5817 or 1N5819 Schottky diode (D1) Capacitors 1 10µF 16V PC electrolytic 5 1µF 50V monolithic (multilayer) ceramic 1 100nF 50V monolithic (multilayer) ceramic 2 22pF 50V ceramic disc Resistors (0.25W, 1% metal film) 1 10kΩ 4 100Ω Connectors & cable 1 10-pin dual-row shrouded (boxed) PC mount header (CON1) 1 10-pin IDC cable mount socket 1 9-pin IDC female ‘D’ connector 1 6-pin 2.54mm pitch single-row PC mount header (CON3) 2 6-way header sockets to suit CON3 1.5m 10-way IDC cable (for serial cable) 250mm 6-core data cable or 6-way rainbow cable (for ISP cable) 50mm (approx.) 0.71mm tinned copper wire (for links) Additional parts for 10-way ISP cable (optional, see text) 1 10-pin dual-row shrouded (boxed) PC mount header (CON2) 2 10-pin IDC cable mount sockets 250mm 10-way IDC cable Additional parts for bootstrap programming (not required if IC2 is supplied pre-programmed) 1 6-way header socket to suit CON3 1 25-pin male ‘D’ connector 1 2-pin 2.54mm pitch single-row PC mount header (JP1) 1 jumper shunt (for JP1) 450mm 6-core data cable or rainbow cable Fig.9: you only need to make this cable if your micro’s (IC2) Flash memory is “blank”. Bootstrap programming is a once-only job, so your work doesn’t have to look too pretty www.siliconchip.com.au software we’ve selected is called “PonyProg”, and it’s available free from www.lancos.com PonyProg runs on Windows 95, 98, ME, NT4 and 2000 and requires only minimal hardware. After installation, power down your PC and connect the bootstrap programming cable. One end connects to CON3 on the programmer and the other to your PC’s parallel port. Install a shorting link on JP1 and hook up the external 5V DC power source (watch the polarity). Hold your breath and switch on. Now power up your PC and launch PonyProg. You’ll see messages to the effect that “setup” and “calibration” need to be run before proceeding, so let’s do that first. The following functions are all accessible from the menu bar at the top of the main window. First, select Setup -> Interface Setup. In the window that appears, choose the “Parallel” option. In the drop-down list, October 2002  77 Fig.10 (left): PonyProg can be configured in just a few seconds. Our “bootstrap” programmer is compatible with Atmel’s STK200/300 parallel port programmer, identified here as an “AVR ISP”. Don’t check (tick) any of the “Invert” boxes! Fig.11 (right): this is what you should see after successfully loading the program (.HEX) file. choose “AVR ISP API” if you’re running Windows 95, 98 or ME, or “AVR ISP I/O” if you’re running Windows NT4 or 2000 (see Fig.10). Click on the OK button to close the window. Next, select Setup -> Calibration. Follow the displayed instructions to run the calibration. To complete the basic settings, select Device -> AVR Micro and choose your micro from the long list of supported devices. Before “burning” the micro, you need to load the program code. Select File -> Open Program (FLASH) File. From the “Files of type:” drop-down list, change “*.e2p” to “*.hex”. Next, navigate to wherever you unzipped AVR910a.ZIP (or AVR910b.ZIP, see above) and double-click on the appropriate .HEX file. The .HEX file is loaded and displayed in the edit window (see Fig.11). OK, it’s programming time. Select Command - > Write Program (FLASH) and the Status window appears. If all goes well, you’ll get a “Write successful!” message. If you get an error message instead, use the Command -> Erase function and try again. Once you’ve managed to successfully program the micro, close PonyProg, power down your PC and disconnect the programming cable. Switch off the 5V power source and remove the associated hook-up wire, as well as the shorting link on JP1. All done! done with sidecutters or a sharp knife (mind the pinkies!). The PC board should now slide all (or most) of the way into the case. As the board nears the bottom, it should “wedge” in place, held firmly by the sides of the case. For a more permanent installation, you can attach the board to the bottom of the case using 6mm stand-offs, 10mm M2.5 screws and M2.5 nuts. For ribbon cable exits, file small flat slots in the lip of the case so that the cables just fit when the lid is closed. If you’ve used data cable for the 6-way ISP cable, file an appropriately sized slot in the lip on one end, or alternatively, drill a hole and fit a grommet. Using the programmer The AVR ISP Programmer integrates with Atmel’s AVR Studio as well as a number of other commercial development packages. AVR Studio can be downloaded free of charge at ftp://www.atmel.com/pub/ atmel/astudio3.exe No special configuration is required to get your programmer working with AVR Studio. Simply connect the RS232 cable to a free COM port (COM1 Housing A little surgery is required in order to fit the completed assembly in the specified case. Cut away the integral card guides of the case so that you’re left with reasonably smooth internal surfaces. This can be 78  Silicon Chip Fig.13: same-size PC board artwork. Fig.12: AVRprog is invoked within AVR Studio by holding down ‘Alt’ and hitting ‘9’. to COM4 is supported), connect the ISP cable to the target board and apply power. To activate the programmer from within AVR Studio, hold down the ‘Alt’ key and press ‘9’. The “AVRprog” window should appear, (see Fig.12). A stand-alone version of the programming software is also available. Download it at ftp://www.atmel.com/ pub/atmel/aprogwin.exe Die-hard DOS fans can download a DOS version from ftp://www.atmel.com/pub/atmel/aprogdos.exe Want to know more? Atmel’s application note titled “AVR910: In-System Programming” should be consulted first. You’ll find it on Atmel’s web site at www.atmel.com For details on programming specific microcontroller types, refer to the data sheets, available from the Atmel site. SC www.siliconchip.com.au