Re: Starting P21Forth

[Louis Frazier <cogniscu@xxxxxxx>]

I am quoting a message to me from Andrew Sieber In the hope that it and
my responses may help others and elicit comments of help to all of us:

> I assume you're not actually
> hooking the video out from the P21 to the PC monitor.  

Correct, I'm not. I use a collection of old PC parts cobbled together as
a 386.
I'm writing this on my Power Mac. The 386 is in my sloppy studio, the
Mac in my wife's office. I find I can do all my 386 stuff in Softwindows
(using DOS) on the Mac when I want to.

> Are you using a serial or parallel interface?
 
Serial. I'm sure it isn't efficient because of the loops needed to
monitor the receive port, but it works fine now that I've increased
volatage. Once I'm building self starting embedded systems, I can turn
off the monitoring while the real work is being done. I built an
adjustable supply with an LM317 (and three resistors) from a design in
an old ham manual. I'm running at about 5.6 volts and my memory works
fine and doesn't seem to get too hot. I don't know what would happen to
it in an application where it ran 24-hours a day. The two supply
approach might work. If paging slows things down, I might design a sytem
where most of the work gets done on one page. Ting's manual gives lots
of tantalizing clues on system building.  

> I assume that the old P21 did still work, even after running at the
> higher voltages?  Was the oscillator the only thing that quit?

I checked the original p21 again and it doesn't work now, but I must
have damaged it when I damaged the oscillatoor (or blasted it with
finger static), because I never deliberately ran it at  more than 4.95
volts. The replacement seems very happy and quite cool after several
hours of running and working at 5.6v

>  I'm using a breadboard and a soldering iron, but it looks like
> I'm going to have to redo the whole thing with either a neatly
> wirewrapped circuit (which will take quite a while) or a PC board, which
> will take a while to lay out.   I wanted to breadboard the whole thing,

I find wire wrap is faster than point to point solder. When I can't get
wire-wrap sockets (as in DRAM and plcc) I wire wrap where I can and
solder (with a very small iron)  the other ends if necessry.That's the
way I've built 8088 and V25 systems on perfboard. To fit plcc sockets
into perf board, I cut a hole the right size, wrap the edge of the
socket with copper tape and line the hole with copper tape and solder
the socket into the hole. (Same technique as Tiffany lamps and church
windows.) Since my boards are part of my art, I also work pieces of
glass into the board. The copper tape makes convenient  ground. 

>... inductance/capacitance problems I may have with my horrid-looking
> rat's nest breadboarding job I did.

I read in a (MAXIM?) manual that crows foot wiring is much better than
neat wiring because of cross talk. Horrid looking probably works best
and is easiest to do.

> Of course I could just buy the thing from Offete, but I want to do it
> myself. 
 
I'm a penny pincher myself, but I feel I have to spend money to learn by
getting something up and running quickly. Then I can experiment. Ting
sells a board and a plcc p21 and documentation for about $125. Dram is
now down to $35 and the other components are peanuts. Or you could get
the assembled job and documentation for $275 and be up and programming
quickly. I had trouble because I had to learn about the 5.5v the hard
way. Starting out with that, I would have been coding in a couple of
hours. 
 
> Also see my MISC list message I'm sending now regarding my P21 troubles.

You shook a lot of good stuff out of the trees with your message. That's
the value of users' groups!
 
 Thanks Louis