View Full Version : Sym-1

December 5th, 2006, 02:02 PM
Thought I'd tell you about the new member of my family. A Synertek SYM-1 in poor condition, but which I managed to get going anyway.

I found it in my TAFE college's soldering lab which is a mess of old computers, VCR's and TV's. I was quite happy to find it as I had found the manual for it last term. It was put out with a heap of books for people to help themselves to, which I promptly did when I realized I could. Got some Motorola 680x0 manuals and CMOS databooks out of it too.

The condition of the SYM-1 is poor. It had been used for soldering practice, which is why it was in the soldering lab. I said to my lecturer I found it and he asked if I wanted it, I was quite happy that day :).

It was missing the keypad, the 6502 was dead and someone had tried to replace the original MOS ROM's with standard Intel ones, which aren't quite compatible. The keypad I replaced with a bit of prototype board with tactile buttons and some paper taped to it. The ROM's I replaced with 28C256's (32K, I'm getting some 8K ones soon), where I bent out some pins and put loops of wire to where the correct pins should be. Works a treat now. It runs Synertek BASIC and RAE which I downloaded from 6502.org.

I love the oscilloscope output feature. I made one for my 8080 when I first found the manual, but the original is the best. It works on the behavior of the brightness depending on the speed of the sweep. The edge of a good square wave is blank and the rising edge of a sawtooth is visible. Knowing this, if you have a sawtooth wave and enable it onto the oscilloscope during the rising edge at the correct times, you can get an almost vertical line with gaps in it, provided the sweep is slow. Adjust the gaps correctly and you get graphics. Not very good graphics but graphics none the less. The advantage is it's very easy to implement, about 5 transistors, but it needs a lot of attention from a CPU, or better yet a microcontroller, to make the display work.

Here's a photo of the circuit running on my 8080. http://kaput.homeunix.org/~thrashbarg/crt_display2.jpg



nige the hippy
December 5th, 2006, 02:07 PM
wow well done,

It's always nice to get an abandoned find going again.

And a "hello world" application into the bargain.

December 5th, 2006, 05:37 PM
Way cool, Thrashbarg! I just bought a Sym-1. I can't wait to play with it!


nige the hippy
December 6th, 2006, 04:41 AM
Incidentally, have you got the circuit, or a link to the circuit for the scope display, would be nice to pop in the "useful things" folder.

December 8th, 2006, 11:15 AM
Incidentally, have you got the circuit, or a link to the circuit for the scope display, would be nice to pop in the "useful things" folder.


To operate it get the data for the next line and shift it through point B, when you've shifted 8 bits, pulse point A. This will reset the vertical sweep. When all of the lines are drawn (160 is the standard, 32 characters at 5 lines) pulse point A for a very long time, enough to create a noticeable pulse on the oscilloscope. This pulse is used to sync the display to the sweep. If you set the oscilloscope trigger to negative edge then the pulse itself won't be visible at the start of the sweep, so you'll just have text.