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Motorola 68HC912B32

    The 68HC12 series of microcontrollers is an upgrade to the 68HC11 commonly used in robotics as the controller on the popular Handiboards and Botboards and many other homebuilt boards.  The HC11 series was a good processor for robotics.  The HC12 series provides more speed, memory and I/O capability while being upwardly compatible with the HC11 instruction set.

    The HC12 has the disadvantage of only being available as a surface mount chip, hence making it difficult to make your own boards unless you are quite experienced.  However, the chip is available from several manufacturers already built onto a board.  The particular implementation that I will present is the Adapt912 built by Technological Arts in Toronto (www.technologicalarts.com).

Adapt912.jpg (334783 bytes)    The Adapt912 provides all the additional hardware necessary to get the HC912B32 running:  Voltage regulator, RS232 interface, power on reset control, and all I/O pins are brought out to a connector.  TechArts provides an adaptor in their starter kit which permits the Adapt912 to be plugged right into a standard protoboard.  This makes it very easy to interface to many types of sensors and actuators with no additional circuitry and just using jumper wires on the protoboard; or even to construct  interface circuitry right on the protoboard.

    Click on picture to enlarge.

    The basic HC912B32 chip has 32K or Flash memory.  The top 2K is used for a bootload program permitting the rest of the Flash (or other RAM or EEPROM) to be programmed over a serial bus from your PC.  So, 30K is available for user code.  My firefighting robot has over 50 pages of C code in it and is using only 22K of the 30.  The chip also has 1K of RAM and 768 bytes of EEPROM.

    TechArts also has a 64K RAM expansion board available which can be convenient during development or for expanded data storage.  But, you don't NEED it to do serious programming.

    There has been some concern that the Flash memory could only be erased and programmed for a limited number of cycles (a few hundred).  There has been quite a bit of discussion of this on the internet; and the consensus seems to be that the "few hundred" cycles is a real worst case scenario.  Many people (myself included) have gone far beyond a few hundred and have experienced no failures.

    The 912 has a large number of I/O pins (63).  The 8 analog input pins can be initialized for continuous Analog to Digital (ATD) conversion.  Hence, you do not have to do any inline code to accomplish each ATD input.  Just read the latest value from a memory location.  The 4 PWM outputs are completed programmable and can be set up so that you just have to store a number  to memory to update the PWM duty cycle.  It has a good number of timers and input capture/output compare pins.  Almost all pins not being used for a special I/O feature (e.g. PWM) can be set up as general discrete I/O pins.  The 912 has many interrupts, both external (2) and internal (timers, ATD, captures, etc) as well as a real time clock interrupt.

    Almost all the input pins have internal programmable "pull-ups" saving a little external circuitry.

    The "Starter Kit" version of the Adapt912 provides the Adapt912 card, a connector to attach power to the card, the adaptor plug to interface the card to a protoboard, hardcopy documentation for the 912B32 chip, and a CDrom with much additional info including Motorola's freeware assembler, Karl Lunt's Sbasic compiler and many coding examples..  A freeware C compiler is also available.  The TechArts website provides links to many additional sources of information and coding examples including Motorola's large collection of on-line documentation.

    With the software supplied with the starter kit, you can immediately hook the board up to a 9 volt battery, attach a standard serial cable from the board to your PC and bring up the built in monitor/debug software which comes preinstalled in the Flash memory.  You can use the Windows accessory "hyperterminal" to communicate.  You can then copy the Sbasic and Assembler from the CDrom to your computer and start programming.  Install the board onto a protoboard and you can start attaching sensors and servos.

    With all this said,  the Adapt912 may not be the place for a neophyte programmer to start.  You must understand or learn a fair amount about how a microcontroller works to get going.  All the information and examples is available, but it's a much bigger jump to get going than a Basic Stamp.

    But, if you already are an experienced programmer, or are bumping into the performance limitations of the Stamp, the Adapt912 provides a big leap in performance capability for a reasonable cost.

   If you are interested, I recommend you go to their website and investigate all the information available (mostly in the "resources" section).