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The prototype SocketBoard is shown here connected to a genuine Atmel AVR ISP programmer. It also works with the AVR in-system programmers described in SILICON CHIP in October 2001 & 2002. AVR ISP SocketBoard Teamed with an AVR in-system programmer, this board enables you to program Atmel microcontrollers on the spot – without an expensive production programmer or development system. It supports just about all dual-in-line AVR micros and includes overcurrent protection. M OST ATMEL AVR microcontrollers can be programmed via their in-built serial programming interfaces (SPI). This method is ideal for in-situ programming, such as might be used in manufacturing or for firmware development or field upgrades. In this scenario, the micro remains in its socket on the application board and a low-cost in-system programmer (ISP) is plugged into a dedicated programming header. In other words, the microcontroller does not have to be removed from its socket and plugged into a parallel programmer each time a firmware update is required. However, in some cases it is desira64  Silicon Chip ble to program a microcontroller standalone, such as when the application board is unavailable or doesn’t include an ISP (or JTAG) header. A low-cost method of stand-alone programming might also be useful where a batch of chips is needed for a small prototype run and the cost of a commercial parallel programmer is prohibitive. This is where the AVR ISP SocketBoard comes in. It provides the minimum of functions necessary to support in-system programming, including a regulated power supply, clock source and microcontroller IC socket. Just connect your in-system programmer to a PC, plug its ISP cable into the By PETER SMITH SocketBoard’s on-board header and add a DC plugpack. You’re then ready to start programming! Programming sockets As you can see from the photos, the SocketBoard contains five programming sockets. Why so many? Well, we’ve provided one programming socket for each group of micros with common SPI pinouts. This allowed us to eliminate the switching logic that would have been required if we’d used just a single, 40-pin socket, so greatly simplifying design and construction. We expect that many constructors will install just one or two programming sockets (depending on their requirements), to keep costs as low as possible. The overlay diagram (Fig.2) lists specific device types and the sockets (SK1-SK5) that support them. For example, to program the ATMega16, socket SK4 must be installed. For cases where quantities of chips need to be programmed, the board will accept standard zero insertion force (ZIF) sockets as well. There is absolutely no need to install ZIF siliconchip.com.au Fig.1: the SocketBoard consists of a current-limited power supply, oscillator, ISP header and a series of programming sockets. This simple configuration supports most dual-in-line packaged AVR micros. Surface-mounted equivalents can be accommodated by using commercial DIL adapters. sockets (as shown in our photos) for occasional programming; this would simply be expensive overkill. The unit can be powered from a 12V DC 150mA (or higher) unregulated plugpack, which also powers the ISP programmer when it’s plugged into the on-board header. Operation As mentioned, the SocketBoard provides the minimum of functions necessary to support in-system prosiliconchip.com.au gramming. As stated, this includes a series of programming sockets to accommodate the different types of AVR micros, a regulated power supply, and a clock source. The power supply is based around two series-connected LM317 adjustable positive regulators (see Fig.1). The first regulator acts as a current limiter. In normal operation, it performs no function. However, should the current through R1 increase to a level where about 1.25V is dropped across it, REG1 begins to reduce the voltage at its OUT terminal. In effect, REG1 then acts as a constant current source, limiting output current to a maximum of 125mA. In normal operation, the complete setup consumes an average of about 20-40mA, depending on the type of in-system programmer connected. The remaining capacity (85-105mA) leaves a comfortable margin, which in most cases is still low enough to preserve any micro that might be accidentally reversed in a socket. It also protects other components if an internally short-circuited micro is plugged into a socket. The second regulator (REG2) is March 2006  65 Fig.2: follow this diagram closely during assembly. Take particular care with the orientation of the electrolytic capacitors, D1, LED1 and IC1. Also, be sure to install the 10-pin header (CON2) with the keyway facing towards the programming sockets. Note that although we show ZIF sockets in five positions, most constructors will require only one or two for high-volume programming. Fig.3: the full-size etching pattern for the PC board. It can also be downloaded from the SILICON CHIP website. 66  Silicon Chip siliconchip.com.au Suitable Programmers This project has been tested with three programmer variants, as follows: • SILICON CHIP In-System Programming Adapter, as described in the October 2001 issue. This very low cost programmer connects to your PC’s parallel port. It’s still available in kit form from Altronics (Cat. K-2885). • SILICON CHIP AVR ISP Serial Programmer, as described in the October 2002 issue. For greater compatibility, this programmer connects to your PC’s serial port. It’s available as a kit from Jaycar Electronics (Cat. KC-5340). • AVR ISP Programmer. This genuine Atmel item is supplied preassembled and again, it connects to your PC via a free serial port.You can purchase these from JED Microprocessors, phone (03) 9762 3588 or browse to www.jedmicro.com.au This is the completed prototype. Make sure that all parts are correctly oriented. configured as a conventional voltage regulator. Without JP1 installed, it produces +5V to power the system. Installing JP1 reduces this to +3V. Some constructors may find this lower voltage useful for verifying the memory in micros that are destined for 3V systems. Note, however, that the two SILICON CHIP in-system programmers are not designed for operation at 3V; you’ll need the genuine Atmel programmer for that job. As well as power, AVR micros require a clock source for their internal programming circuits to operate. This is provided by a Pierce oscillator, which is composed of a 4MHz crystal (Y1), two resistors and one gate of a 74HC04 hex inverter (IC1a). A second gate (IC1b) buffers the clock signal before it is applied to all of the programming sockets. A 47W resistor provides series termination and current limiting. All that now remains to be described is the ISP interface. This is extremely simple indeed, as it consists only of a 10-pin DIL header (CON2) and five resistors. The four 100W series resistors act as peak current limiters, in case the ISP cable or a chip is accidentally inserted with power applied. These also help to protect the programmer if a faulty micro is inserted in a socket. The remaining resistor (47kW) pulls siliconchip.com.au down the interface’s RESET line, so that the micro is held in the reset state if a programmer is not connected or is non-functional. Assembly Using the overlay diagram (Fig.2) as a guide, install all the low-profile components first, starting with the wire links and resistors. There are seven links in total, all of which can be fashioned from 0.7mm tinned copper wire or similar. Follow with all of the capacitors, noting that the leads of the 10mF and 100mF units must be bent at right angles before installation. Before bending the leads, check that you have the positive leads oriented correctly. The crystal (Y1) also mounts horiz­ ontally, so bend its leads about 2-3mm from the can before installation. Once in place, a short length of tinned copper wire should be soldered to the top of the can and the pad directly below to secure it in position. Diode D1, LED1, header CON2 and the 14-pin socket for IC1 can now go in. All of these items are polarised, so make sure that they’re installed the right way around. Don’t plug the 74HC04 into its socket just yet, though; it’s a good idea to test the power supply first (see below). All of the remaining items can now be installed, leaving the five programming sockets (SK1–SK5) until last. The two LM317 regulators (REG1 & REG2) should be attached to the PC board using M3 x 6mm screws, nuts and flat washers. As shown, their leads must be bent at right angles before installation. Be sure to tighten the screw & nut before soldering the leads, otherwise damage to the regulator package or PC board may result. The three 2-pin headers (JP1-JP3) can be cut down from a longer section using a sharp knife. Check that each header is sitting square on the PC board surface before soldering. Finally, install just the programming sockets (SK1-SK5) that you require. For casual use, low-cost IC sockets can be installed in any or all of the indicated positions. Alternatively, ZIF type sockets can be fitted to any positions that are expected to be high usage – it’s up to you. Testing Connect a 12V DC source to the DC socket (CON1), noting that the centre pin is the positive input. If the power connections are accidentally reversed, nothing bad will happen as a series diode provides polarity protection. Now apply power by sliding S1’s March 2006  67 Par t s Lis t 1 PC board coded 07103061, 145 x 105mm 1 4MHz crystal (HC49 package) (Y1) 1 DPDT PC-mount slide switch (S1) (Altronics S-2060, Jaycar SS-0823) 1 10-pin dual-row shrouded (boxed) PC-mount header 1 2.1mm PC-mount DC socket (CON1) 2 20-pin IC sockets (SK1 & SK2) 1 28-pin IC socket (SK3) 2 40-pin IC sockets (SK4 & SK5) 1 6-pin 2.54mm (0.1-inch) SIL header strip (for J1-J3) 3 jumper shunts 6 M3 x 6mm pan head screws 2 M3 x 6mm nuts & washers 4 M3 x 10mm tapped spacers 160mm (approx.) 0.7mm tinned copper wire (for links) Note 1: if desired, small stick-on feet can be used in place of the tapped spacers. Semiconductors 1 74HC04 hex inverter (IC1) 2 LM317T adjustable voltage regulators (REG1 & REG2) 1 1N4004 diode (D1) 1 3mm high-brightness red LED (LED1) Capacitors 1 100mF 25V PC electrolytic 1 10mF 16V PC electrolytic 1 220nF 50V MKT polyester 5 100nF 50V monolithic (multilayer) ceramic 2 22pF 50V ceramic disc Resistors (0.25W, 1% metal film) 1 1MW 1 300W 1 47kW 1 120W 1 1.8kW 4 100W 1 1kW 1 47W 1 360W 1 10W Note 2: low-cost ZIF sockets in all of the designated sizes are available from www.futurlec.com. Higher quality units of various types are available from www.dontronics. com and www.rockby.com.au actuator towards the edge of the board. The power LED should light immediately. If it doesn’t, either the power connections are reversed or there is an assembly error. Carefully recheck the 68  Silicon Chip 8-pin devices are programmed in the first 20-pin socket (SK1). Here’s how they’re inserted, with pin 1 in the same position as for 20-pin devices. Note that jumper shunts must be installed on JP2 & JP3 when programming 8-pin devices. board against the overlay diagram and look for dry or missed solder joints. Next, use your multimeter to measure the voltage between pins 7 & 14 of IC1’s socket. Expect a reading of 5V ±5%. Temporarily insert a jumper shunt on JP1 and measure the voltage again. This time, you should get the lower reading of 3V ±5%. When done, remove the jumper, as in the majority of applications, a 5V supply is preferred for programming. If the power supply checks out, switch off and insert IC1 into its socket. Naturally, the position of the notched (pin 1) end of this IC must match that of the IC socket. Using it It doesn’t take a lot of grey matter to use the SocketBoard. Simply switch power off, plug your in-system programmer into the AVR ISP connector (CON2), and insert the microcontroller to be programmed into the designated socket. After switching on, the micro can be programmed following the instructions supplied with your ISP. Important: always switch the power off before inserting or removing a microcontroller from its programming socket. Note that 8-pin micros present a special case. Instead of a separate socket, all 8-pin devices are programmed in the first 20-pin socket (SK1). In addition, jumper shunts must be installed on JP2 & JP3 to route signals to the correct places for these diminutive devices. After programming an 8-pin device, the two jumper shunts (JP2 & JP3) should be removed if you also intend to program 20-pin devices in the same socket. This ensures that there is no possibility of damage to the larger devices. If a faulty micro is inserted in a socket or if a working device is inserted backwards, the current-limit function will swing into action. In most cases, the current passed through the part should not be destructive – if the problem is noticed right away and power SC is switched off! Warning! Programming the “reset disable” fuse present on some smaller AVR devices disables the RESET input, with the side effect of preventing further programming via the SPI port. In other words, you’ll no longer be able to use your in-system programmer to erase, read, write or verify the affected part. To restore SPI access, the device must be erased on a parallel programmer, high-voltage serial programmer or JTAG programmer, depending on the device in question. Do not experiment with fuse settings unless you know exactly what they do! siliconchip.com.au