Hello,

I have an old Synertek Sym-1, and I am very intrigued on the topic of the built-in oscilloscope output. I wrote out the software driver and added in an external trigger where the manual said to (pb4), and I've probed the trigger and video signal and they work. The vectors, when you plug them in, seem to keep the board functioning and the "display", when hooked up, seems to change as said in the manual.

HOWEVER

I am completely unable to figure out how this is supposed to look, or how I'm supposed to read any characters on the oscilloscope display. The ramps look way too sharp, and I am just really lost at this point.

Attached are images of the triggered display and nontriggered display.

Welcome!

I see there's a previous mention and a successful demonstration of this circuit in an earlier thread:
Hopelessly Simple SYM-1 Oscilloscope Driver
and fortunately the wayback machine has saved one of the screenshots:


However, I can't say I really understand how it's done - somehow an interrupted sawtooth creates a raster output. There are only two wires: sync, and display. This is not a TV scan or an X-Y mode.

We're directed to chapter 7 of the manual, which has some diagrams and explanation, but I don't quite get it.
https://deramp.com/downloads/mfe_archiv ... f#page=106

Edit: perhaps this helps


In other words, the raster is a series of steep up-sloping lines, which we think of as vertical. The lines are interrupted by clamping to zero which is why we see a strong flat line below the one-line display.

Over on the VCFed forums, thrashbarg writes

I'll take a look, and yes, I have used the included driver in the manual, which is what my oscilloscope output shows.

That photo is very very promising!

(Edited my reply slightly!)

I think you might need to set your scope so it doesn't draw the steep vertical lines which return the raster to the zero baseline. You need to see just the tops of the pulses.

Edit: You need a very slow timebase, of 50ms.

I recall having done this on my SYM-1 with a very old scope in 1981. If I recall correctly it looked about like the picture of the display. The details are lost in the mists of time. I have the same scope now as you have, but I had removed enough parts from that circuit on the SYM to reclaim the PB2 line for the clock signal in a keyboard driver that I created for Cortron keyboard with serial non-ASCII output. I'm not sure that I could make the scope interface work again to try it out. I still have the SYM-1 (now with a KTM3-80 but the Cortron is gone). I would commend you to look at the topic on Symbiosys (viewtopic.php?f=2&t=1696) for connecting a CF card interface to your SYM. (Needs RAE though).

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

As for Symbiosys, I have looked at it and I have built up the card and ssd, however, I couldn't get it to work lol. I instead am using an edited SYMDOS with a few extra routines. I will definitely try to use symbiosys in the future!