# [EVDL] Basic Stamp replacement - Parallax Propeller



## EVDL List (Jul 27, 2007)

Hi all,

This message will be of interest to those using Basic Stamps or other 
microcontrollers to build stuff for their EVs. See for example Lee 
Hart's Battery Balancer.

I did a project last term with a Parallax Basic Stamp. I was 
impressed with the ease of programming, but not very impressed with 
the sluggish performance and the relatively high cost. I also was 
driven insane by the lack of interrupts, and the paged memory model, 
and especially by the lack of a timer.

This term I'm doing a project with a Parallax Propeller. You can see 
the same design philosophy, but this chip is waaaay further along the 
Moore's Law curve. Faster, more capable, and cheaper.

More info here: <http://www.parallax.com/tabid/407/Default.aspx>

Briefly, it has eight processor cores running at 80 mhz each. 
There's a native assembly language, but there's also a new 
interpreted language on board called Spin that's more advanced than 
PBasic (crude support for objects, etc.) There's an Object Exchange 
on the Parallax web site that has lots of code objects for free 
download. Plus, a free (speech+beer) Basic compiler (called 
PropBasic) has just been released that is very similar to Pbasic 
except that your programs run much faster. There's a version of C, 
Forth (of course), and a bunch of other neat stuff. There's a multi- 
platform IDE called bst that works fine on my old Mac.

The chip comes in a 40-pin package with 32 I/O pins. Each core has 
access to all of the pins, as well as its own RAM and some counter 
and timer hardware.

There's no extra hardware on the chip. For example, there's no 
physical UART. The idea is that you code one up and run it on its 
own core. This works really well - for example, there's a software 
object you can download that makes one CPU core into a video driver 
(composite or VGA). Anyone want to code up a video dashboard? The 
"video card" hardware is three resistors and a connector.

My development board came as a kit and cost about $40. One Propeller 
chip, one 5mhz crystal, one voltage regulator, one serial EEPROM, one 
capacitor. The Propeller chip costs $8 direct from Parallax (or 
Digikey). (I got the dev board from <http://www.gadgetgangster.com/ 
>. They have one that's almost identical to an Arduino.) If you 
want something more like the Stamp with all the parts on board 
(including a USB interface), Parallax makes one of those too for $80.

Let's see, what did I forget? Oh yeah, 32kb of shared ram. Each 
core gets an additional 2k of private ram. Access to the shared ram 
is round-robin with only one CPU allowed access at a time, which 
solves a lot of concurrency problems. 32k of ROM that contains the 
Spin interpreter, character sets, trig tables, and a few useful 
things like a UART driver to talk to the IDE at boot.

Still no interrupts, but who cares? Put your task on its own CPU and 
let it run concurrently, with predictable timing and no worries about 
reentrant code.

The only reason I can think of to get a Basic Stamp is for backwards 
compatibility... oh wait, they've got a Propeller Stamp that's got 
the same form factor. Never mind.

Disclaimer: I have no financial interest in Parallax, I'm just an 
excitable nerd.

--
Doug Weathers
http://www.gdunge.com
"There is no easy way from the Earth to the stars." - Seneca
"We choose to go to the Moon and do the other things - not because 
they are easy, but because they are hard." - John F. Kennedy



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