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A Tiny Plug In Computer using MSP430FR2xxx devices

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Last week, I introduced a tiny language, called SIMPL,  I have been working with for a while. Now I'd like to introduce some hardware - that I hinted upon last week.





ChipStick is possibly one of the smaller dev boards you may encounter - it's intended to plug into a 20 pin DIL socket - which makes it both breadboard and Launchpad friendly.


At it's heart is one of the new MSP430FR2xxx series devices with 15.5kbytes of FRAM and 4Kbytes of RAM.


These controllers come in a tiny 4mm square 24 pin QFN surface mount package, making them a bit awkward to prototype with - so that's why the idea of ChipStick was developed - a small carrier pcb which converts the SMT part into a plug-in DIL 20 package.


ChipStick also comes with its own programmer section - based on the low cost CH340G USB to serial converter IC. This allows communications between the IC and a laptop, and also allows it to be programmed serially using the uart based BSL programming option.


The programming section is detachable - so you can have just the 20 pin DIL module if you want to go extra small.  


In this format the board is small enough to fit inside a 2x4 LEGO block!




In addition to the MSP430 there is also 32K x 8 bytes of external SPI SRAM or FRAM (depending on your application). The MSP430FR2xxx series have 3 communication interfaces and the 25xx and 26xx parts have capacitive touch capability too.


One of the aims of ChipStick is to teach electronics and computer science.  Whilst it is not the fastest device the external memory allows virtual machines to be investigated and the high speed SPI allows shift registers to be used for extending the I/O - for driving LED arrays or stepper motors or whatever peripheral electronics you wish.


ChipStick may be programmed using Energia, CCS or a high level language such as Forth, including MECRISP, 4E4th or Amforth.


My inspiration came from another small computer, the PDP5 from 53 years ago.




ChipStick offers about the same computing resources as the PDP5, but for $5 not the $50,000 the PDP5 cost in 1963!



The first batch of ChipStick pcbs have been ordered. After Easter I should have something up and running, at which point the EagleCAD files will be made available.








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  • 2 weeks later...



The programming section is detachable.  The pcb is perforated with a line of 0.5mm holes so that the end section can be cut off - or snapped off.


With the programming section detatched, you can then use a 1.27mm connector pair and plug it back into the other end of the board.


In effect, every ChipStick comes with a free programmer and USB-Serial converter.





In the underside view, above, you see the CH340G  (about $0.40) it's 12MHz crystal and a couple of 22pF capacitors.  On the topside is the 3V3 voltage regulator and some more decoupling capacitors (10uF, 100nF).


The programmer uses a 6 pin  1.27 mm connector  - but NOT the pinout of the TI version - because if you get the TI connector in backwards you will fry your target.


The connector looks like a half size FTDI pin-out (with the exception TEST is an output) and carries the following:


1  0V


3  VCC

4  RX

5  TX



TEST is driven from the DTR signal and /RESET is driven from the /RTS signal. 






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By "programmer" we're talking serial bootstrap loader, of course... not Spy-Bi-Wire JTAG emulator.

It would probably be a simple matter to produce an adapter board with the 1.27mm pinout on one side, and either a 14-pin TI MSP-FET header or a special line of pins designed to plug right into an eZFET header on a launchpad to enable both UART and SBW for this.

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It did actually start off at the other end of the board - which initially seemed a good idea at the time, but for tracking reasons, the SPI RAM needed to go there too - and in the end the RAM won the toss.


With hindsight - it could be easily moved back again - now that all the traces are in place. Perhaps that's something for Issue 2.  There are also 2 unused pins on the processor which could also be tracked out, a 24 pin DIL footprint might be a better overall size - allowing more features.


This is a BSL programmer and comms interface  - it is not a FET. If you want to do FET or SBW  debugging then you need to use one of the more recent Launchpads (such as 4133 5739, 6869  etc) and connect 0V, /RST and TEST  - that will allow SBW programming and debug.


I have nothing against FET/SBW - except that it is a big lump on the end of a dev-board,  and ChipStick is all about lightweight design. Having the USB interface detachable - but re-deployable by way of a cable and connector gives the greatest flexibility.






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