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PICAXE Update Many SILICON CHIP readers enjoy using the PICAXE range of microcontrollers within their projects because of their low cost and ease of use. Clive Seager, Revolution Education’s Technical Director, takes us through the recent PICAXE updates and new releases, including the eagerly anticipated new PICAXE-20X2. AXE027 PICAXE USB download cable AXEpad software When the PICAXE system was first developed over ten years ago the ‘9 way serial port’ was the conventional way of connecting the computer to external devices, such as digital cameras. The now-familiar PICAXE ‘3.5mm jack plug/socket’ connection was selected as (1) it is robust and (2) many early digital cameras used exactly the same serial download cable, meaning the cables were a low-cost mass produced item! USB has now taken over this role and most modern laptops now only have USB-style connectors. Unfortunately, the USB protocol is far more complex than the serial RS232 protocol; in fact it is not possible to implement the USB protocol on low-cost, limited-memory devices like 8 and 14-pin PICAXE microcontrollers. There simply isn’t enough memory space to implement both the USB protocol and the PICAXE firmware! Therefore an alternate approach is required and that is to use a separate ‘intelligent’ USB cable with an embedded USB-to-serial converter chip, such as those made by FTDI. This gives the best of both worlds – a USB connection to the computer and a serial connection to the PICAXE chip itself. As you can see, the AXE027 download cable contains a complete miniature circuit moulded into the USB connector. This allows the cable to work via USB on all Windows, Linux and Mac computers. To support PICAXE users who wish to use Linux or Mac computers to develop their PICAXE BASIC programs the new cross-platform AXEpad software is now available (Windows users should still use the Programming Editor software). When combined with the AXE027 USB download cable AXEpad provides a complete development system for Linux and Mac users. AXEpad has been deliberately designed with a small footprint and so will also work well on low-cost flash drive Linux ‘netbook’ computers such as the eeePC. As you would expect AXEpad supports all the common PICAXE features such as colour highlighting of BASIC programs and in-built testing features such as the ‘Debug’ and ‘Terminal’ functions. AXEpad is completely free of charge and will operate with: • Linux – any modern x386 distribution with GTK2.8+ • Mac – OSX (10.3 or later) on PowerPC or Intel machines siliconchip.com.au November 2009  63 Logicator flowcharting software Current PICAXE chip lineup Logicator is a flowcharting application widely used within UK schools and colleges for over twenty years for developing control programs. Over the years PIC microcontroller technology has vastly improved, resulting in more memory capacity and features. This has enabled the PICAXE chips to be enhanced with additional commands, more RAM variables and additional memory capacity, all at a lower cost! The full PICAXE lineup is shown below: Current PICAXE range Entry Intermediate (100-200 lines) (600-2000 lines) 08M 14M 18M 18X 20M 28X1 40X1 Enhanced (2000-3000 lines) 20X2 28X2 40X2 New X2 range All program development is performed graphically by joining flowchart shapes together, and so is simpler for younger students to use than BASIC style ‘textual’ programming languages. Recently Revolution took over the Logicator product and have spent the last 12 months bringing it up to date to support all the current PICAXE chips. The software is now also distributed as unrestricted ‘shareware’ and so anyone can download it from www. picaxe.co.uk and try it out without charge. So if you have always been a bit daunted by BASIC programming why not give flowcharts a go! Logicator is very easy to use and also supports onscreen simulation that allows simple testing of flowchart operation. If desired the flowcharts can also be automatically converted into BASIC program listings.  ƒ          ƒ   X2 Enhancement Summary: • Each pin can now be individually configured as input or output • Up to 12 internal ADC channels available • Up to 256 general purpose RAM bytes • Up to 1024 additional bytes in the RAM scratchpad • Indirect RAM access to support easier use of arrays • Clock speed ups to 64MHz, 16x faster than 4MHz! • Wider operating voltage range (1.8 - 5.5V), ideal for 3V systems • Up to 4 internal program slots – allowing up to 10,000 lines of code with 1000 sub-procedures! • Also supports up to 32 more program slots stored in external EEPROM chips • Support for UNI/O brand EEPROM chips using a single i/o line • New hardware interrupt pins • New comparator functions to compare 2 ADC channels    ­  
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„ ‚  „ The new PICAXE X2 range (20X2, 28X2 and 40X2) is a complete new generation of the PICAXE chip, making use of the advanced features and architecture of the newly released PIC18F series of microcontrollers. The entire PICAXE core has been completely rewritten to provide a more flexible and higher specification tool for more advanced projects. Although the features and memory capacity have greatly increased, prices have not – for instance the new 20X2 is the same price as the older 18X part!                   
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 ­      Pinout comparison between the new “X2” PICAXE chips. As you can see, functionality has been preserved (as much as possible) between the chips. X2 chips can easily be used to upgrade existing projects. 64  Silicon Chip   ­  ­     €‚ €ƒ           
   
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   siliconchip.com.au X2 Enhancements • RAM • I/O Pin Flexibility One of the key new features of the X2 series is that almost every pin is configurable as input or output. This creates much more flexibility with circuit design as you are not fixed to a pre-defined ratio of inputs to outputs on any chip size. Naturally the pins can also be configured to the ‘traditional’ PICAXE layout if desired. • Analog Inputs Many more ADC channels, up to 12, are now available on a number of the i/o pins. This again provides greater flexibility with circuit design. New comparator features also allow two analog channels to be compared, so that an interrupt can occur if one analog value exceeds another. • Greater Processing Speeds The 20X2 can operate at up to 64MHz via it’s internal resonator. This is a vast speed improvement – for instance a program that took 2 minutes to process on an 18X at 4MHz will now take less than 8 seconds! This is ideal for systems that need rapid response times, such as persistence-ofvision LED display systems. • Increased Voltage Operating Range The 20X2 will function from 1.8V all the way up to 5.5V, making the single part ideal for both 3 and 5V systems. This large voltage range is quite a technical breakthrough, and is achieved via a new innovative design – a 3V silicon core combined with an internal integrated low dropout regulator. This means that the 3V core, which would normally only tolerate 1.8V to 3.3V, can be used all the way up to 5.5V because the internal regulator ‘kicks-in’ when required and constantly maintains the internal core voltage at 3V. • Hardware Interrupt Pins The X2 range has up to 3 pins that can be configured as hardware interrupt pins. When configured, these pins continuously background scan for an edge based trigger, even during sleep. When this trigger occurs a flag is set which can be used to trigger a special ‘interrupt’ section of BASIC code. The X2 parts have a much greater RAM capacity, 256 bytes on the 20X2 and 1280 bytes on the 28X2/40X2. This increased memory capacity allows much more complex calculations and programs. X2 parts also accept indirect memory access via pointers (<at>ptr, <at>ptrinc, <at>ptrdec), which is ideal for building arrays of data. • Program Slots The 20X2 has 1 program slot, the 28X2/40X2 have 4 internal program slots. Each X2 program slot can contain approximately 2000-3000 lines of BASIC code. When the microcontroller is reset the program in slot 0 automatically starts running. The other programs can then be started by using a ‘run’ command. • External Slots As well as the internal memory slots, 4 additional slots can be used by connecting an external I2C EEPROM chip. As up to 8 different I2C chips could be used on the same I2C bus, this gives a theoretical 32 additional program slots with over 64,000 lines of BASIC code! • UNI/O Support The X2 support communication with external Microchip UNI/O EEPROM memory chips. The advantage of uni/o memory is that it only requires 1 microcontroller pin, as opposed to I2C which requires 2 and SPI which requires 3. Summary As you can see 2009 has been a very busy year for us at Revolution Education and we hope you enjoy using the new PICAXE software and parts. As ever, if you have any feedback or new feature requests please do not hesitate to contact us via www.picaxe.co.uk – almost all new PICAXE features are the direct result of PICAXE community feedback! All software described in this article can be downloaded free of charge from www.picaxe.co.uk, while PICAXE cables and chips are available in Australia from www.microzed.com.au and in New Zealand from www.sicom.co.nz. They are also available from several electronics stores. SC JOIN the teChNOLOgy age NOW WIth PICaXe Developed as a teaching tool, the PICAXE is a low-cost “brain” for almost any project. Easy to use and understand, professionals & hobbyists can be productive within minutes. Free software development system and low-cost in-circuit programming. Variety of hardware, project boards and kits to suit your application. Digital, analog, RS232, 1-Wire™, SPI and I2C.PC connectivity. Applications include: Distributed in Australia by 1[Datalogging 1[Robotics 1[Measurement & instruments 1[Motor & lighting control 1[Farming & agriculture 1[Internet server 1[Wireless links 1[Colour sensing 1[Fun games Microzed Computers Pty Ltd Phone 1300 735 420 Fax 1300 735 421 www.microzed.com.au siliconchip.com.au www.siliconchip.com.au NEW X2 HIPS now in sC tock! November 2009  65 2009  67