Single board computer

[bbcmicro]

Recent activity on this forum has again made me want to build my own single-board computer, a wish expressed in a (much) older post.

I have been looking around, and I thought a good system to try was the Cosmac Elf, rather than designing my own which is waaay above my head. I was especially swayed when I read about the MicroElf kit (http://www.elf-emulation.com/) which would save me from painful wiring, BUT, they are sold out and the 1802 processor seems hard to get hold of, never mind all the parts.

Right now, I am looking for a minimalistic computer that just provides the basics, with cheap parts and not thousands of connections. However, preferences include programmability (Not just a flashing LED) and some sort of display (Binary or digital, doesn't matter) and potential expandibilty.

I realise I am being specific, and I don't really know what I am doing, but why not make a start now?

Any suggestions as to well documented projects?

[mbbrutman]

Have you considered starting with something just a little higher level, like the BASIC STAMP?

http://www.parallax.com/html_pages/p...sic_stamps.asp

[nige the hippy]

I re-started off (after many years gap) with the basic stamps. First using the modules, then making boards for the chip & separate memory, it was from having problems (corrupting programs in a commercial environment) with them, that I had a look at the chips, discovered they were PICs and started programming PICs in machine code, still using the same boards, and the same chips, but putting the code in myself.

There are various PIC basic compilers and PIC "C" around and you're welcome to a home made pic development board for the PIC16F84. dead easy code to learn, with only a few quirks. Flash memory >1000 times programmable, In circuit programming on 5V, (there are some software parallel port programmers available, but I haven't used them) I've got some spare chips, & leds too. Thinking about it I have routines for driving small LCD displays (and displays) Have a look at the datasheet & see what you think. Also pic programming skill is VERY saleable.

I know it's not quite vintage, but you can always move backwards.

Alternatively look out for a "micro-professor 1" (MPF1) it was a great little Z80 dev kit, obsolete, but fun. Expensive on Ebay, but occasionally findable on computer fairs.

[ahm]

Isn't Arduino the new Basic Stamp?

[bbcmicro]

PIC programming would be very useful. We use PICs in our Systems and Control classes in school, although considering the majority of our class inept, we are removed from the entire programming and manufacturing process. We are just given the finished PCB, the PIC and components, and told to solder them together, then whatever you are making (I am making a score-keeping table top golf game using a PIC and a LDR for my GCSE) works like magic. I think it's a shame.

It would be nice to learn how to use them and how they work. It would also be a good rung on the ladder to learning how to handle EPROMs (And more probably EEPROMs in my case, no expensive UV box!) Which I intend to do as soon as a sort out the spaghetti lingo they use, which chips are most common and which I would actually use. And when I can afford a programmer!

Incidentally there is a rather nice 8 bit ISA card for XT with and EPROM programmer, but the bids are getting rather high.

I have watched a couple of complete Micro-Professors with docs, binders etc. go on eBay for £50+ with envy. I want one!

The BASIC stamp in the form of something like this: http://www.parallax.com/detail.asp?product_id=28103 seems like a good start. But, like a lot of things in this hobby the price is too steep for me. (I can't wait till I get a job this summer! then I can afford the things I want ) Drawing on Nige's experience with BASIC stamps, I think learning to use PICs would be a good start, then move up (Or down, chronologically!).

I am curious about the BASIC stamps though, could one easily interface a keyboard/pad, and LCD display to these and use them as a computer in their own right with only 32 bytes of RAM?

Thanks for the input! Keep it coming, I'm learning loads today!

[nige the hippy]

Yes, it's surprising what you can do with 32 bytes. (consider how many variables you use in the average small basic program!)

The bigger PICs have a bit more memory, and some have EEPROM you can use yourself.

As far as interfacing a keyboard to a "stamp" or a pic indeed, it's pretty straightforward, a 16 key keyboard can be done with 8 pins 4 in and 4 out in a matrix (and you can double up the 4 outputs to drive LEDS etc) the stamp also has serial in and out routines so you can use a terminal, You don't even need to use any hardware except a capacitor on the output to drive from a PC because you can select the serial routine to invert the output (ie more like a low level RS232) if neccessary.

[sjv]

Hey. This is a vintage board, right? Are PIC's vintage?

The COSMAC ELF is a cool computer. I built this one:

http://www.sparetimegizmos.com/Hardware/Elf2K.htm

Mike Riley (elf-emulation) doesn't make ELF boards anymore because this design is a little nicer. Mike does contribute a LOT of GREAT software for this platform, though. I also built the RTC/NVRAM/CF Card board to go with it. I am partial to the CDP1802, though, having built my own COSMAC Elf from the PopTronics articles back in 1978, when I was 14.

There's a great yahoo group dedicated to the Elf:
http://groups.yahoo.com/group/cosmacelf

I am also eyeing the Apple1 replica board here:
http://www.brielcomputers.com/

I have a fondness for the 6502 CPU, as it was the 2nd CPU I learned to program on (A PET 2001).

-steve

[bbcmicro]

Again, the problem of price comes up. I did see the spare time gizmos kit a while ago, but getting all the parts costs well more than I can afford. Vbriel's replica 1 especially. Uber cool, but with an Uber pricetag

Would a keyboard matrix need another IC, or could it be interfaced directly to the stamp to carry out basic funtions?

I really am starting to like the sound of the stamp, it sounds like a gentle learning curve, and easy(ish) to interface to. But again, I can't afford it, unless I get a stamp on its own which seems impractical for a beginner like me with no means to use it.

Nig, could you expand on your home made development board? It sounds blinky and cool but I'm not going to pretend I know what it does!

In preparation for the construction of a computer that may never happen, I have a book from thhe early 80's called "Microprocessor Interfacing" about nearly everything I could want to know about the Z80, 8080A, 6502 and 6800...if only I understood all of it! I do however get the gist, but any technical detail is lost on me.

Matty.

[nige the hippy]

Yes I appreciate that pics aren't exactly ancient, but it is a means to an end. If it'll get Beeb going on micros, on pocket money, all well and good. We all use modern english (and occasionally 133t 5p33k ??) here as a means of conveying information, if we all used ancient greek, it would be a truly elite and very tiny forum.

And... I stand corrected, I just WIKI'd the pic micro, and find it dates from 1975, and in it's modern form, 1985.... truly ancient. Actually when I started programming them, they were well established & it was on a relatively 'modern' 486DX2-66, using dos based tools downloaded from a bulletin board.


oopps been message hopping, just off out, but I'll expand on my dev board & other kit in email form tomorrow.

[Thrashbarg]

There is a crapload of information over at www.6502.org if you want to use the 6502 CPU.

I would recommend it for a first single board computer because it's a very simple processor (that and I love it) and doesn't have the legacy problems of the Z80 from the 8080. There are a lot of instructions that don't make much sense on the Z80 because they're based on 8080 instructions.

The only tricky part is memory mapped devices but this is easily solved with a few 74LS138's, but this makes a full 64K RAM a little difficult to achieve, unlike the Z80/8080. This usually isn't a problem if you're using your own ROM monitor and not a full OS. It's almost required on the 8080/Z80 if you want to run something like CP/M.

The BBC Micro is 6502 based if I recall correctly