Re: Starting P21Forth

[Louis Frazier <cogniscu@xxxxxxx>]

Andrew:

I bought Dr. Ting's wired and populated P21 Card and have been working
with it. I get it to write on the screen of the 386 i use as the monitor
and also to show a blank screen on an ntsc monitor (Apple II green), l
but it doesn't accept characters from the computer keyboard after the
prompt, except for a few occasionally. Sometimes 2 2 + . will produce a
normal 4, CR ok.

I talked to Dr. Ting and he suggested I look at my power supply. He says
p21's are happiest at 5.5 volts. Makes the sram run hot, but improves
the ntsc signal display. I haven't found the perfect combination yet. I
did discover that my 14.8 mhz oscilator was not putting out a wide
enough swing. I may have damaged it fooling with power supplies. In fact
I repopulated the whole board with dram, etc from Jameco and a new p21
from Offete because I was getting nothing. As soon as I put in the new
chips video and prompt took off. I reinstalled the old chips one at a
time and found the bum oscillator. 

I am considering building an adjustable 5v power supply because none of
the old pc and ttl stuff I have lying around goes more than a couple of
mv above 5.

It seems as though I ought to be able to feed the p21 5.5 and the rest
of the chips 5 if heating cooks the dram too badly. P21 runs only
slightly warm to the touch at 5v.

I'm glad to find someone else willing to approach Forth with a soldering
iron
and wire wrap tool. Once I learn how these things work, I intend to wire
wrap my own boards to run my artworks.
( see http://www.artswire.org:70/1/COGNISCU )
Feel free to email me directly at cogniscu@tmn.com if you like.

Note to Penio Penev: I'm running a Roland U220 synth with MIDI from my
present board design which is an embedded FORTH system built on a NEC
V25. I would be interested in sharing any MIDI interests we have in
common. I want to switch to p21 because it is faster, drives an NTSC
monitor, needs fewer support chips but has lots of memory, and has much
a better programming environment ready made. I think I can accomplish a
lot with p21s, and upgrade easily when f's or I's x's come along. I hope
we can find lots of music shareware.