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layout: page
title: Challenger 1P Programming Guides/Samples
permalink: /pubs/c1p/programming/
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Challenger 1P Programming Guides
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Challenger 1P Programming Samples
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### 6502 ASSEMBLER/DISASSEMBLER

This "source code listing" from June 19, 1980 is for the first piece of software I sold, right around the
time I graduated from high school.  I had had my Ohio Scientific Challenger 1P for maybe a year when I decided
to write something that would make it easier to write "machine language" programs than the incredibly tedious
HEX monitor that was built into the C1P.  And so my **6502 ASSEMBLER/DISASSEMBLER** was born, with full-screen
editor, assembler, and disassembler.

One of the conditions of the sale, however, was that I provide a "source code" listing.  I don't think the buyer
understood that I had essentially written the program in machine language -- because that's how I had to enter it
into the machine.  Maybe *some* lucky C1P users had disk drives and editors and assemblers, but I had none of those
of things.  I had never even used tools like that before, which is why the **6502 ASSEMBLER/DISASSEMBLER** is a
bit of an odd duck.  I'll post some screenshots and a demo eventually, and you'll see what I mean.

Anyway, to satisfy the buyer, I sat down at my old manual typewriter and banged out my version of a "source
code" listing.  I produced it mostly by using the program to disassemble itself, combined with information
from hand-written notes (which I may still have somewhere).  Here it is, many decades later, for your amusement.

[<img src="http://archive.pcjs.org/pubs/c1p/programming/thumbs/OSI_Assembler-Disassembler_Listing-thumb.jpg" width="200" height="260" alt="6502 Disassembler Listing (by Jeff Parsons, June 1980)"/>](http://archive.pcjs.org/pubs/c1p/programming/pdfs/OSI_Assembler-Disassembler_Listing.pdf)