P21

[Andrew Sieber <asieber@xxxxxxx>]

Jeff Fox wrote:
> debugging your rig:
> 
> first try just P21 and a ROM and clock to start with and see if it
> passes tests 0, 1, and 2.  Then do 0-6 with DRAM.
> 
> 0. does the oscilator produce a 14M wave?
> 1. does it access the rom when it boots?
> 2. does it read lots of stuff from the rom at boot?
> 3. does it write lots of stuff to dram at boot?
> 4. does it start generating a video signal (all black) durring boot?
> 5. does it display P21Forth in the center of the screen for a while?
> 6. does it read the keyboard?
Unfortunately, the only test equipment I have is a multimeter and a
flaky 5MHz oscilloscope that's older than I am.  #0: I tested the
oscillator by hooking its output to six cascaded 74161's (4 bit
counters), and the output of the last cascaded 74161 to an LED.  I
calculated that the LED should flash at approx 4/5 Hz, and when I
applied power the LED did indeed flash at about 4/5 Hz.  Of course this
doesn't tell me how clean the oscillator's square wave is, but it does
verify that the oscillator is oscillating.
#1 & 2:  I could hook the SRAM# (ROM) pin of the MuP21 to my 74161
cascade and watch the outputs of the 74161's on LEDs to see if they
count real fast.  That would tell me whether lots of ROM access is being
done.
However I have decided to etch a circuit board and try again with it in
a couple weeks, since I can then be positive that I don't have a loose
connection, wiring mistake, etc.
>From what you've said that I'm doing correct (ROM burn, schematic,
etc.), that should work.  If not, I will go into detailed analysis of
that circuit board and run all of the tests you described above.
Right now I feel pretty sure that I must have a loose connection, or a
short somewhere in the SIMM socket I soldered wires to, or a wiring
error, etc.  To give some idea of the wire tangle I have right now, I
can't put my finger on top of the P21 (or any other chip for that
matter) without ripping wires from the breadboard to get to it.  I
really should have just etched a circuit board to begin with.
Speaking of etching circuit boards, I decided to use a shareware CAD/PCB
layout program called Easytrax.  Has anyone else used this program?  Is
there any standard file format that everybody uses for CAD/PCB layout
work?

Dave Lowry wrote:
> 
> I think Jeff Fox deserves some public thanks for the *free* P21 support
> he's giving on this mailing list.
Yes and I feel kind of bad because I've been a recipient of a bunch of
free P21 support and I've contributed nothing to the advancement of
MISC.
I do "advertise" Pegasus to teachers at my school though and perhaps can
generate a couple of sales when the device becomes available.  :-)  They
currently pay $2500+ for Pentium machines to dedicate to nothing but
internet access for the school, a task for which Pegasus will be
perfectly suited.  From rough numbers I've heard, they can get about ten
Pegasus machines for the price of one of their Pentium machines.  They
are impressed by those numbers!  And there are already TVs in all of the
classrooms so they don't even have to buy separate TVs for the Pegasai
(plural Pegasus?)
I'm still a drain on resources though (time specifically) with my
questions.  Sorry about that.

Louis Frazier wrote:
> 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
That's the FIRST report of a dead P21 I've ever heard.  From reports
I've heard of backwards power and heating the chips past 100 degrees
centigrade without destroying it, I think these chips will leave Mr.
Energizer Bunny in the dust.

> 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.
I don't know about other sockets, but I know I can wire-wrap to the SIMM
socket that Jameco sells that is intended for soldering to a PC board. 
It makes a pretty good connection.

> >... 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.
Assuming you hook everything up right to begin with.  If you're like me
and are dumb enough to use all one color wire everywhere, it's
impossible to tell after the fact where all the wires are running. 
Either it works, or you start over.

> > 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.
Not only the penny-pinching aspect (which I really ought to be ashamed
of since I'm getting valuable free support on this list), but also I
want to see for myself exactly how everything goes together.  As soon as
I get the basic system up and running and experiment with P21Forth a
little, I intend to start adding/changing stuff and writing my own
software, both P21Forth-based and from-scratch.  Then I can really
understand P21 programming inside and out.
When I get my PCB etched in a couple of weeks I'll post results here,
positive or negative.

--Andrew