Issue 142 May 2002
Taking a Swim with Atmel's STK500

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Start • The Atmel STK500 • Imagecraft AVR C Compiler • Sources & PDF

THE ATMEL STK500

The meat of my Atmel STK500 starter kit is shown in Photo 1. The AVR-supporting electronics are physically and logically separated into three distinct areas on the printed circuit board. The most colorful area is where the target AVRs reside. You can program a variety of AVRs in these color-coded sockets and then run the freshly programmed application without having to move the target AVR.

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Photo 1—The color-coding scheme on the Atmel STK500 starter kit assumes you were present the day your kindergarten teacher taught the basic colors. Color coding the numerous sockets and programming headers eliminates some of the confusion, as the STK500 is one busy piece of electronic equipment.

Each family of AVRs has a different set of programming pins and possibly a different programming algorithm. To accommodate the program mode differences, the Atmel STK500 development board associates a color-coded set of programming header pins with a similarly colored set of target AVR sockets. The STK500 board has provisions for in-circuit serial programming (ISP), high-voltage serial programming, and high-voltage parallel programming.

High-voltage serial programming is used on the smaller devices that don’t have enough pins to be programmed with the parallel method. The "high voltage" is actually 12 VDC and is usually applied to the RESET pin of the AVR. In addition to the target AVR sockets, jumpers to include or exclude target AVR operating and reference voltages, oscillators, and crystals are also found in the color-coded area. All of the AVR socket signals are brought out to expansion headers in case you have bigger plans than the STK500 development board can handle on its own.

A set of eight LEDs and corresponding push-button switches are located at the end of the board opposite the 9-pin D shell connectors. There are also headers for target AVR I/O ports, the spare RS-232 port, and the AT45D021 2-Mb Data-Flash. A collection of interconnect cables is included to patch in the AVR ports and peripherals. Two 10-pin jumpers are used to connect I/O ports to the LED/push-button bank, and the 10-pin cables are also used in high-voltage programming mode. A 6-pin jumper cable is included to patch the 6-pin ISP programming header into the AVR socket farm. The AT45D021 communicates using SPI and there are three sets of two-conductor patch cables to make that connection. The spare RS-232 channel is also a two-conductor patch.

The peripherals and the master microcontroller (an AT90S8535) can be found at the end of the board that sports the DE9 shell connectors. This section of the STK500 development board is well populated. Without going into component-by-component detail, I can tell you that the master microcontroller is responsible for generating the VTARGET and AREF voltage levels using PWM outputs that are passed through low-pass filters to the adjust pins of a couple of LM317 linear voltage regulators. A master clock for the AVR targets also originates in this area of the board.

The DE9 shell connectors imply serial communications capability, and a MAX202 does the RS-232 voltage level conversion that allows the STK500 development board to attach to a desktop PC running AVR Studio. Atmel likes to call AVR Studio the front-end software.

Although I’m primarily interested in getting the ATmega16 online, I decided to keep the AT90S8515 socketed and run the LED test. I pressed each of the eight push buttons and with each push got a different light pattern on the LEDs. On my second run through the push buttons, I noticed that the seventh push button did nothing. When there’s potential trouble, it’s time to go against the grain and read the User Guide. The final pages of the guide hold the code for the LED demo, and there I found out that push button number seven is not included in the LED algorithm. Satisfied that my STK500 development board was in good working order, I went to Atmel’s web site and downloaded the latest version of AVR Studio.

AVR STUDIO

As of this writing, the latest version of AVR Studio is V.3.53. The AVR Studio is an integrated development environment (IDE) that consists of an editor, a project manager, an assembler and compiler interface, a simulator, and a debugger. The AVR Studio editor is capable of being coupled with almost any AVR compiler and C or assembler source code can be edited in the debugger source window.

If AVR Studio recognizes anything that is hanging off the PC’s serial port, the program automatically puts itself in a mode to accommodate the serially attached peripheral. For instance, AVR Studio can sense the presence of my Atmel STK500 development board or an emulator and act accordingly.

To keep things simple, the interface for the AVR Studio simulator is identical to the hardware emulator interface. AVR Studio V.3.53 is designed to enable the Atmel STK500 board without the need for any additional software. AVR Studio also includes firmware to update the development board and AVR in-circuit emulators when necessary. AVR Studio checks the attached device’s firmware level and prompts the user if a firmware upgrade is required.

I’ll use some available resources to bring AVR Studio to life and demonstrate some of the concepts I’ve discussed. The larger AVR Studio panel you see in Photo 2 is the first thing you see when you invoke the AVR Studio program. At this point, my Atmel STK500 development board is connected to a PC via the RS-232 CTRL connector on the board. As you can see in Photo 3, I have also strapped the ISP6PIN header to the red SPROG3 header because the AT90S8515 resides in a red socket in the AVR target area.

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Photo 2—The AVR Studio panel looks barren when there are no files or projects open. However, its ability to interface and control the target AVR is demonstrated by its invocation of the STK500 programming window. As we go further, the importance and power of the AVR Studio will become obvious.

 

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Photo 3—The two larger ribbon cables are connecting the LEDs and push-button switches to the AT90S8515’s I/O ports B and D. The smaller ribbon cable enables ISP programming using the AT90S8515’s internal SPI interface.

 

A mouse click on the AVR IC icon in the AVR Studio tool bar invokes the STK500 programming window. As you can see, I’ve chosen the AVR target to be the AT90S8515. I’ve strapped the STK500 development board for ISP Programming mode and have selected that mode in the STK500 programming mode panel as well. I’m not going to program the AT90S8515. Instead, I’m going to read the demo code it contains into a file called blinky.hex.

The final uploaded file location is specified in the Flash panel of the STK500 programming window. A click on the Read button in the Flash panel turns the green STK500 board status LED yellow while the contents of the ’8515 are read. The debug window containing the hex and disassembled code from the ’8515 in Photo 4 confirms that push button number seven does nothing in the blinky demo code.

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Photo 4—All I needed to do was load a live file and almost all of the AVR Studio lights came on. The AVR Studio did not sense a hardware emulator or STK and automatically reverted to Simulator mode.

AVR Studio opens up memory, processor cycles, I/O states, registers, and even a terminal I/O window. Now that you have a basic idea of how the AVR Studio and STK500 board work together, let’s move beyond blinking LEDs and assembler mnemonics and swim toward deeper water.