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Pt.2: By ED SCHOELL* Managing Director, JED Microprocessors Pty Ltd. Assembling and programming the AVR200 Single Board Computer Last month, we published the circuit details for JED Micro’s new low-cost ATmega32 development board and described the various I/O options. This month, we show you how to assemble it and go on to describe several popular software development and programming options. A SSEMBLY OF THE AVR200 is quite straightforward as the PC board is a plated-through, doublesided design with solder resist on both sides. To reduce component count and simplify construction, most resistors are contained in single-in-line (SIL) arrays. 84  Silicon Chip In its standard configuration, the board provides eight analog inputs or digital inputs/outputs, 11 digital inputs and nine Mosfet outputs. Also included are a real-time clock, buffered I2C port and RS232 serial port. If the standard port I/O arrangements are not suitable for your application, then most port lines can be swapped from inputs to outputs or vice versa with only minor component changes. It is therefore important to examine the various options carefully before starting assembly, to ensure that the correct parts are installed from the outset. We covered the various options in detail last month. In summary, the kit contains all of the components needed to configure all available port lines (28) as inputs, if desired. Eight of these can be either analog or digital inputs, with the remainder being digital only. Note that the remaining four port bits of the ATmega32 are dedicated to the I2C and RS232 serial interfaces. Conversely, if more than the standard nine port lines are required as outputs, then up to 12 additional Mosfets can be installed for a full complement siliconchip.com.au Fig.5: use this diagram as an aid when assembling your board. Socket strips are needed for resistor packs RP2RP7, with all others being soldered directly into the board. Of the six packs, only RP5 & RP6 are installed in the standard configuration shown here. To install optional items, follow the silkscreen overlay printed on the board and the instructions in the text. of 21 outputs (still giving seven digital inputs). The extra Mosfets are not included in the basic kit but can be ordered separately from JED. Preliminaries To help make construction easier, we’ve organised our description into logical steps, first assembling the components common to all configurations. We then separately describe the assembly of the components needed for each port (A-D) in turn, with the standard configuration shown first and the optional configuration (if any) immediately after. We recommend that you map out your desired I/O port configurations, including requirements for any additional features (eg, RS485 port and high-resolution voltage reference) and read the entire assembly instructions before commencing construction. Power supply The power supply section should be assembled and tested first. Begin by installing the LM2940T voltage regulator (U3). It mounts horizontally on the board, so first bend its leads at siliconchip.com.au 90° about 6mm from the body and trial fit it into position to ensure that the hole in the tab lines up with the large hole in the PC board. Adjust the lead bend as necessary, then position the TO-220 heatsink between the regulator and the PC board (see photos). Finally, fasten the assembly in place using an M3 screw, nut & flat washer before soldering and trimming the regulator’s leads. All other components related to the 5V power supply should now be installed. These are the 2-way terminal block (J1), DSS706 filters (LC1, LC4LC8), all 100nF monolithic capacitors and the four 33mF tantalum capacitors. Note that the positive leads of the tantalum capacitors must go in as indicated on the overlay diagram, otherwise they’ll be destroyed in a flash at power on! The power indicator circuit, consisting of the LED and 1kW resistor (R7), can also go in now. Now connect a 6-18V DC power source to the input terminals on J1 (note polarity) and power up. Check for correct operation of the power supply by measuring the voltage between the ground and output terminals of the regulator (U3). You should get a reading of between 4.75V and 5.25V. Note also that the LED power indicator should light. Common assembly Rather than a conventional 40-pin socket, the ATmega32 (U2) is mounted in two 20-pin socket strips. As with all other headers and socket strips used in this project, these must be cut down from the longer sections supplied in the kit. This is done using a sharp utility knife or a pair of side-cutters. When installing the socket strips, make sure that they’re seated all the way down on the PC board and at right angles to it before soldering. Once that’s done, install all of the components that go underneath the microcontroller. This includes the TL7726 hex clamp ICs (U5 & U6), the real-time clock IC (U7), 32kHz crystal (X2) and 100mH inductors (L1 & L2). As usual, take care with the orientation of the ICs and zener diodes. Note that U5, U6 & U7 must be soldered directly into the board. Don’t use IC sockets, because it will not be possible to fully insert U2 later on. July 2005  85 Fig.6: both “common” and “series” single-in-line resistor packs are used in this project. Here’s how they’re wired internally. As you can see, orientation is important with the pullup/pull-down type, with pin 1 being the common connection point for the resistor array. Next, install reset switch SW1, the DS1233 reset IC (U1), the 3.6864MHz crystal (X1) and the 27pF capacitors. The crystal is supplied with an insulating washer that fits over its leads to isolate the underside of the package from the PC board. Make sure that this is in place during installation. Note also that the “arrow” on the top of the reset switch should point towards the “RESET” marking on the overlay. To complete the common part of the assembly, install all of the connectors and headers, including the screwterminal blocks (J2-J5 & J9-J12), the D9 connector (J8), I2C headers (J6 & J14), SPI header (J13), and links L13-L18, with attention to the following: Before installing J13, cut pins 7-10 off flush with the plastic carrier using side-cutters or pull them out with a pair of pliers (see Fig.5). Note that J13, J14, L13 and L14 are cut down from longer dual-row header strips, whereas links L15-L18 are cut down from single-row strips. Port A – analog/digital inputs (standard): install eight 7-pin socket strips in locations L4-L11. Again, these are cut down from the longer strips supplied in the kit. Various components are plugged into the strips to perform basic signal conditioning functions ahead of the port inputs, as described in Pt.1. 86  Silicon Chip At a minimum, each input should have a series resistor (see Fig.4a) to protect the microcontroller (in conjunction with the TL7726 voltage clamps). Eight 10kW resistors are provided in the kit for this purpose. Port A – digital outputs (optional): the socket strips (L4-L11) are also installed if you wish to use port A as low-current digital outputs. In this case, a small resistor (about 100W) should be inserted in series with each output (see Fig.4a). The socket strips must not be installed if you want to use port A as high-current Mosfet outputs. Instead, the Mosfets and their 10kW gate pulldown resistors (Rpd) are soldered directly into the PC board in place of the socket strips (see Fig.4f). Note that the Mosfets are not supplied in the kit but can be ordered separately from JED, part number MTD3055VL. Important: while it is possible to mix digital inputs and outputs on port A, it is not recommended to mix analog inputs and digital outputs, as noise from the outputs may cause inaccuracies in analog readings. Analog reference (standard): if the +5V (Vcc) supply is to be used as a voltage reference, link L3 must be shorted by “blobbing” it with solder. Conversely, if the internal +2.56V band-gap reference is to be used, the link is simply left open and the selection is made under program control. Precision analog reference (optional): parts for the 4.096V precision reference are optional and can be purchased separately from JED as part number AVR200-REFK. Included in the option pack are a MAX874CPA voltage reference IC (U4), 2.2MW and 3.3MW resistors (R1 & R2), 1MW trimpot (VR1), 47nF capacitor (C14) and 4.7mF tantalum capacitor (C15). After installing all of these parts, the output from U4 (pin 6) must be trimmed to precisely 4.096V by adjusting VR1. Port B – digital inputs (standard): to configure port B for all digital inputs, first install 6-pin socket strips in positions RP5 & RP6. A 4.7kW, 5-pin common resistor pack can then be plugged into each of the sockets. As described last month, one end of the socket strip is connected to +5V (pin 6) and the other to ground (pin 1). This means that the resistor packs can be used to perform a pull-up or pull-down function simply by orienting them correctly in the socket strips. Next, install 4.7kW 8-pin series resistor packs in locations RP7 & RP15, and six 4.7V zener diodes in locations Z6-Z9. Make sure that you have the banded (cathode) end of the zeners around the right way. Leave location RP1 empty, as it’s only required when using port B for high-current outputs, as described below. Port B – digital outputs (optional): the upper (PB4-PB7) and/or lower (PB0-PB3) bits of port B can be used as low-current digital outputs, if desired. For example, to use the upper lines as outputs, leave out RP6 and install four low-value series resistors (about 100W) in place of RP7. A similar scheme can be applied to the lower lines. Provision has also been made to use the lower four lines (PB0-PB3) as high-current outputs, if desired. To do this, leave out RP5 & RP15 and install MTD3055VL Mosfets in locations F1-F4. These devices are available separately from JED. A 4.7kW, 5-pin common resistor pack must also be installed in the RP1 position. Naturally, if you decide to expand “upstairs” via J13, then many of these port bits will not be available for general-purpose use on the screw-terminal blocks (J11 & J12). This means that you may be able to leave out some or all of the resistor packs mentioned above. Port C – TWI (I2C) port: the lower siliconchip.com.au two bits (PC0 & PC1) of port C are used for the I2C port. By default, the I2C port is “buffered”, so links L24 & L25 (beneath U11) must remain open. Install the 82B715 buffer (U11), the 1.5kW and 330W pull-up resistors (R3, R4, R9 & R10), and the two 10W series resistors (R11 & R12). The two 4.7V zener diodes (Z1 & Z2) that protect the micro’s inputs should also be installed. If you want to connect non-buffered I2C devices, do not install U11, R9 & R10 but do install the two series resistors (R11 & R12). Note, however, that these must be 100W rather than the 10W values shown on the diagrams. In addition, links L24 & L25 must be shorted by bridging them with solder. Port C – digital outputs (standard): in the standard build, the upper six bits (PC2-PC7) of port C drive power Mosfets to provide high-current opendrain outputs. All that needs to be installed here are the Mosfets (F5-F10) and the two 4.7kW, 6-pin series resistor packs in locations RP8 & RP9. Locations RP2, RP3, RP13 & RP14 remain empty. If desired, all of these bits may also function as low-current digital outputs. In this case, omit all the Mosfets and resistor packs mentioned above and install low-value series resistors (about 100W) in place of RP13 & RP14. Port C – digital inputs (optional): to use PC2-PC7 as digital inputs, do not install the Mosfets or RP8 & RP9. Instead, install two 5-pin socket strips in locations RP2 & RP3. That done, 4.7kW 4-pin common resistor packs can be plugged into these sockets to perform pull-up or pull-down functions, as described earlier. Next, install six zener diodes (Z10Z15) in locations RP8 & RP9. These do not appear on the circuit or overlay diagrams, but are simply soldered vertically into the holes left vacant by the two resistor packs. Check that you have the zeners around the right way; the anode ends connect to the ground plane on the topside of the PC board. Par t s Lis t for AVR200 (Standard Build) 1 AVR200 PC board 6 DSS706 EMI suppression filters (LC1, LC4 – LC8) 1 3.6864MHz crystal (HC49U package) (X1) 1 32.768kHz miniature watch crystal (X2) 1 BR1225/1VC 3V lithium cell (BATT1) 2 100mH miniature axial inductor (L1, L2) 1 sub-miniature slide switch (SW1) 1 10-way 2.54mm pitch DIL boxed header (J6) 1 9-way right-angle female ‘D’ connector (J8) 1 6-way 3.81mm pitch screwterminal block (J3) 3 5-way 3.81mm pitch screwterminal block (J2, J11, J12) 4 4-way 3.81mm pitch screwterminal block (J4, J5, J9, J10) 1 2-way 3.81mm pitch screwterminal block (J1) 2.54mm pitch SIL header strips (see text) 2.54mm pitch DIL header strips (see text) 2.54mm pitch SIL socket strips (see text) 1 M3 x 6mm screw, nut & washer 1 TO-220 heatsink 1 LM2940T-5.0 low-dropout +5V regulator (U3) 2 TL7726 hex voltage clamping IC (U5, U6) 1 DS1307 real-time clock IC (U7) 1 MAX202E RS232 transceiver IC (U8) 1 P82B715 bi-directional I2C bus buffer IC (U11) 9 MTD3055VL logic-level Mosfets (F5 –F13) 18 4.7V 0.5W zener diodes (Z1-Z18) 1 3mm red LED (LED1) Capacitors 4 22mF 10V tantalum (C9-C11, C16) 8 100nF 50V monolithic ceramic (C1-C8) 2 27pF ceramic disc (C12,C13) Resistors (0.4W, 1%) 8 10kW (see text) 2 1.5kW (R3, R4) 1 1kW (R7) 2 330W (R9, R10) 2 10W (R11, R12) Resistor packs 3 4.7kW 4-pin common resistors (RP2-RP4) 3 4.7kW 5-pin common resistors (RP1, RP5 & RP6) 6 4.7kW 6-pin series resistors (RP8-RP14, RP16) 2 4.7kW 8-pin series resistors (RP7, RP15) Semiconductors 1 DS1233 5V reset IC (U1) 1 ATmega32-16P microcontroller (U2) Finally, install 4.7kW 6-pin series resistor packs in locations RP13 & RP14. Port D - RS232 (standard): the lower two bits of port D (PD0 & PD1) are reserved for use as the transmit/receive data lines for the serial port. To build the standard RS232 serial interface, install the MAX202 (U8) first, followed by the five 100nF capacitors (C4-C8) if not already in place. Links L20 & L21 should also be shorted by bridging them with solder. In its most basic configuration, the RS232 port does not provide hardware handshaking; the RTS/CTS lines are Table 1: Resistor Colour Codes o o o o o o siliconchip.com.au No.   8   2   1   2   2 Value 10kW 1.5kW 1kW 330W 10W 4-Band Code (1%) brown black orange brown brown green red brown brown black red brown orange orange brown brown brown black black brown 5-Band Code (1%) brown black black red brown brown green black brown brown brown black black brown brown orange orange black black brown brown black black gold brown July 2005  87 Setting The RS232 Port Mode Fig.7: links L13 & L14 are used to set the RS232 port mode. The default configuration is “DCE” with no handshaking, as it allows connection to a PC and use of the MegaLoad software programmer. simply looped back on the D-9 connector by installing a jumper on L14 (the “no handshake” setting in Fig.7). However, provision has been made for hardware handshaking using port bits PD7 & PD6. This feature is enabled by shorting L22 and installing a jumper on L17 pins 2-3. As described last month, the RS232 port can be set for either DTE or DCE modes. The required mode is selected via links L13 & L14, as shown in Fig.7. Port D – three inputs & outputs (standard): of the remaining six bits of port D, three are normally configured as outputs (PD4, PD5 & PD7) and three as digital inputs (PD2, PD3 & PD6). To use PD4, PD5 & PD7 as high-current outputs, install Mosfets F11-F13 and a 4.7kW 6-pin series resistor pack in location RP10. In this case, locations RP4 & RP16 remain empty. If desired, all of these bits may also function as low-current digital outputs. To do this, simply omit the Mosfets and resistor pack (RP10) and install low-value series resistors (about 100W) in the RP16 location. To configure bits PD2, PD3 & PD6 as inputs, install 4.7kW 6-pin series resistor packs in locations RP11 & RP12 and three 4.7V zener diodes in at locations Z3-Z5. Links L15 & L16 allow PD2 & PD3 to be connected to either the screw-terminal block (J9) or the I2C headers (J6 & J14). In addition, link L18 allows the PD6 input to be pulled up or pulled down. 88  Silicon Chip Note that PD6 & PD7 can be redirected to the RS232 port (via links L17 & L22) in support of hardware handshaking, which would make them unavailable for general-purpose use. Port D – swapping inputs & outputs (optional): as with all the generalpurpose I/O ports described thus far, the standard roles of the six port D bits are easily reversed if more inputs or outputs are needed in a particular application. This is achieved in a similar manner to that already described for ports B & C. However, we’ve covered it again here to avoid confusion. To configure bits PD4, PD5 & PD7 as digital inputs, omit the three Mosfets (F11-F13) and install a 4.7kW 6-pin series resistor pack in location RP16. Also, leave out RP10 and install three 4.7V zener diodes (Z16-Z18) to protect the micro’s inputs. Again, these do not appear on the circuit or overlay diagrams but are simply soldered vertically into the holes left vacant by RP10. Check that you have the zener diodes around the right way; the anode ends connect to the ground plane on the top side of the PC board. Next, fit a 5-pin socket strip in location RP4 and plug in a 4.7kW 4-pin common resistor pack. The “common” pin of the resistor pack (pin 1) goes to the grounded end (pin 1) of the socket to pull down the three inputs or to the Vcc end (pin 5) to pull them up to +5V. Finally, to configure bits PD2, PD3 & PD6 as low-current outputs, leave out RP12 and install three low-value series resistors (about 100W) in place or RP11. Port D – RS485 (optional): as men- Where To Buy A Kit Kits and options for this project are available from JED Microprocessors Pty Ltd. A complete price list and order form can be downloaded from www.jedmicro.com.au/ avr200.htm, phone (03) 9762 3588 or email jed<at>jedmicro.com.au AVR200 kit .............................. $99 AVR200 assembled & tested (standard options) ................ $185 Atmel AVR-ISP ....................... $66 Note: all prices include 10% GST. tioned last month, the AVR200 includes support for an RS485/TTL serial port. Parts for this option are available separately from JED (part no. AVR200-RS485K). We do not describe the RS485/TTL serial port here but complete details on installing it will be included on the CDs with the kits and on the JED website. Note also that “revision 0” of the AVR200 board does not support this option, so be sure to mention your requirements when ordering. Finally, those with specific cabling requirements will be pleased to know that there are additional rows of pads at the I/O connector mounting positions to allow for machine or crimpedon plug-in connectors. Again, contact JED with your specific requirements. By now, you should have a fully assembled board, so let’s move on and look briefly at what’s available for application development. We’ll also check out a couple of popular choices for getting your completed code into memory. Software development options We’ve already mentioned that Atmel’s AVR architecture was designed from efficient execution of compiled code. Development packages that allow you to make the most of this advantage are readily available. Atmel recommend a long list of third-party programming packages in their “AVR 8-Bit RISC Third Party Support” document, available from www.atmel. com. Supported languages include C, BASIC, Pascal, Forth and Java. Apart from the Atmel website, another useful resource for AVR programmers is the very active AVR user’s group at www.avrfreaks.net. You’ll find an even longer list of compilers, assemblers and other goodies in the “Tools” section of their site. JED Micro use and support several lower-cost development options. Check out their AVR200 page at www. jedmicro.com.au/avr200.htm for all the details. Free assembler & C compiler For those that need to program AVR micros at the grass roots level, a complete assembler, simulator and debugger is included in the “AVR Studio” software package. The package boasts an integrated development environment (IDE) that allows third-part compliers to be plugged-in as needed. siliconchip.com.au AVR Studio is free and it’s included on the Atmel CD that ships with the AVR200 kit and can be downloaded from www.atmel.com. For the beginner and hobbyist interested in embedded C programming, the free WinAVR GCC compiler offers an excellent, all-round development suite. It has I/O port support, extensive help and embedded support functions for things like delays, EEPROM access, WDT and CRC. It can also produce a debug file for AVR Studio, thus allowing use of the simulation and debugging facilities. Although WinAVR doesn’t include a full IDE like many commercial packages, the “Programmers Notepad” editor can run a “Make” file to automate the whole code generation process. A sample “Make” file is included on the CD with the kit to help first-time users get up and running. WinAVR can be downloaded from winavr.sourceforge. net or check out the links on JED’s website. CodeVisionAVR C Compiler Although at the lower-priced end of the commercial range, CodeVisionAVR from HP Infotech offers ample features and includes a full IDE, including debugger, programmer and terminal. It has library function support for EEPROM access, Dallas 1-Wire, I2C, BCD/Gray code conversion, LCD support, SPI, the Dallas real-time clock and more. Perhaps one of CodeVisionAVR’s best features is the automatic code wizard generator that removes the tedious aspect of setting up your initial register conditions. You can examine all of the other features at www. hpinfotech.ro and browse the on-line user group site at groups.yahoo.com/ group/codevisionav BASIC Compiler If you need results in a hurry and your C skills are a little rusty, then BASIC compilers are worth a look. MCS Electronics offers a powerful commercial compiler for the AVR series. The package, called “BASCOMAVR”, includes a full IDE, including debugger, programmer, simulator and terminal, as well as comprehensive documentation. BASCOM-AVR produces fast machine code, not interpreted code like some other products. It includes library support for EEPROM access, Dalsiliconchip.com.au Fig.8: MegaLoad is an easy way to get your code into the ATmega32 and it’s free! If you request this option when ordering the AVR200, JED will install the necessary bootloader code into the top of the micro’s code memory. las 1-Wire, I2C, LCD, SPI and real-time clock. As a bonus, statements are 99% compatible with Microsoft’s QBASIC. View the product details or download a free demo version at www.mcselec. com. You’ll find an on-line user group at www.grote.net/bascom Readers interested in purchasing the above products will find links to the appropriate sites from JED’s AVR200 page at www.jedmicro.com. au/avr200.htm Programming the micro JED is offering two options for getting your programs into the ATmega32 micro. The first of these requires an additional piece of hardware called the AVR-ISP programmer. This device plugs into your PC’s serial port as well as the 6-pin section of J13 on the AVR200 board. It accepts the hex or binary file output from your assembler or compiler and programs it into the micro’s Flash (program) and/or EPROM (data) memory and sets option fuses all in one operation. The AVR-ISP is supported by AVR Studio and most third-party development tools. However, for those that don’t need to fiddle with the ATmega32’s fuses, the “MegaLoad” bootloader and companion Windows application are a much cheaper option. MegaLoad can be supplied free with your AVR200 kit; all you need to do is tick the right box on your order form. JED will then pre-install it in the top part of the micro’s memory (3C00H) before despatch. To program the micro using MegaLoad, launch the MegaLoad Windows application (supplied on CD) on your PC, connect the AVR200 to the PC serial port and toggle the Reset switch on the AVR200 board. The program code is then transferred over the serial link at 115k bits/second, with no external hardware needed. Wrap up JED Micro are supplying two CDs with all AVR200 boards. One includes all AVR200 circuits, layouts, assembly instructions, a test program with instructions and sample code snippets written in BASCOM Basic and CodeVision C. Also included are MegaLoad and a sample setup and Makefile for WinAVR. The second disk is supplied by Atmel. It contains their complete “Software and Technical Library”, including the AVR Studio software suite, product datasheets, application notes, user guides and source code examples, etc. Now all of that should keep you SC busy for quite some time! July 2005  89