Sunday, March 13, 2016

ChipStick - A Diminutive Dev Board

Chipstick - A complete "Retro" computer on a 40 x 11mm stick

I have recently been looking at the MSP430 as a contender for a general purpose development board. In the last 3 weeks I have looked at several of the extensive range of devices, both the low cost "value line" and other parts, including those with nonvolatile FRAM memory, 24 bit ADCs and LCD drivers. Having absorbed the data sheets of several devices I came to the following conclusions:

1. There are hundreds of MSP variants across several families.
2. Very few packages offer consistent pin-out - allowing one device to be swapped for an upgrade part.
3. Register names and bit names often lack consistency across the various families making common code more difficult.
4. You can never quite find the all peripherals you need in the package you want.

After a bit of consideration, I decided to tackle points 2 and 4 above in one hit - I will design a common carrier board allowing a common footprint.

As I like the small plug-in DIL packages, as they are breadboard and stripboard friendly. So it seemed a sensible idea to use the DIL 20 as a common footprint.  I also found that some devices were available in a very compact 24pin QFN package - which is ideal for mounting at 45 degrees at the centre of a 20 pin DIL footprint.

In my search for the ideal part, I came across the new MSP430FR2xxx series.  These have 15.5K of FRAM and 4K of RAM. In addition they have 2 A type UCSI and 1 B type UCSI universal serial communications interfaces.

So in a few hours, I had designed a tiny carrier board, to which I added a USB to serial converter IC plus some extra features.

Hardware Details

The pcb is designed to take any of the 24pin MSP430FR2xxx range, but in particular the very low cost MSP430FR2433.  The 20 pin DIL footprint breaks out the available pins into a form that can be plugged directly into a low cost Launchpad - in place of the MSP430G2553 device.

This gives almost 16K of nonvolatile FRAM plus 4Kbytes of SRAM - which is eight times the RAM on the '2553.

On the left hand end of the board is the CH340G  USB to serial converter IC. This forms a complete communications and programmer interface - providing the RESET and TEST signals required for the serial bootstrap loader (BSL) programmer.

"Chopstick"  - with the Programmer section removed

It should be noted that this programmer section of the board is detachable, making the 20pin DIL carrier part not much bigger than a standard DIL socket.  A 6 way 1.27mm (0.05") pitch connector allows the programming section to be connected to the target using a suitable cable.

The MSP430FR2433 has 3 very useful communication ports.  One of these is reserved for UART communications to a PC, whist the other two  can be used for SPI, I2C or other GPIO purpose.

The board also makes the following provisions:

1.  A reset switch
2.  A single LED
3.  A 32768Hz crystal may be fitted for more accurate timing.
4.  A lithium battery or super-capacitor may be plugged in to power the board
5. On the underside of the board there is a footprint to allow an external SPI SRAM or FRAM IC to be fitted. SRAM available up to 1Mbit (128Kx8) or FRAM up to 256Kx8.

In the next part, on receipt of the board back from the manufacturers, around March 23rd - I will discuss some applications for this diminutive dev-board.

Other recent Posts on ChipStick

ChipStick - A Diminutive Dev Board

The $5 Forth Computer

First Steps to Building the $5 Computer

Digital Dust

Constructional Guide


Interfacing Memory

I/O Expansion

Graphical User Interface


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