Memory Bus Analysis For 6502 Microprocessor Systems - Info and Reading Options

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<div>A thesis by James D. Moore, published spring 1983.</div><div><br /></div><div>There exists in the world of microcomputers a great</div><div>need to see more of what is “going on" within a particular</div><div>system. This is often necessary for problem solving,</div><div>instructional purposes, program design, and even the</div><div>satisfaction of one's own curiosity. Many programs are also</div><div>"protected" so that even casual analysis is quite impos-</div><div>sible. Program step and trace functions are frequently</div><div>available as software tools but are rendered useless in a</div><div>great many circumstances by protection schemes.</div><div><br /></div><div>The purpose of this project was to develop a simple</div><div>and inexpensive hardware device to assist programmers in</div><div>gaining access to the inner workings of both hardware and</div><div>software. This device is commonly known as a Bus Rider</div><div>when found in development system application.</div><div><br /></div><div>Information on this type of hardware is practically</div><div>non-existent. A literature review revealed only two</div><div>display-type program aids for microcomputer systems, neither</div><div>of which alters the processor speed. The Display Board and</div><div>Bug Lights circuit are useful but rather limited in their<br /></div><div>ability to display information. Both use a series of<br /></div><div><div>discrete LEDs to indicate data, which necessitates a con-<br /></div><div>stant hexidecimal conversion on the part of the programmer.</div><div>They are also particular about when and what they display.</div><div><br /></div><div>Microcomputer systems normally perform several</div><div>hundred thousand operations per second and must. therefore be</div><div>slowed down a great deal to make any sense of the data</div><div>transfer at the bus level. This is possible with the 6502</div><div>microprocessor because it is an early design and was</div><div>required to handle the slow memory devices of the time.</div><div><br /></div><div>The device resulting from this project is</div><div>specifically designed for popular 6502 based microcomputer</div><div>systems like the Apple II. It consists of a synchronized</div><div>clock circuit that pulses the Ready Line of the</div><div>microprocessor and provides variable speed, slow motion, and</div><div>pause capabilities anywhere within an operating program. A</div><div>set of six hexadecimal LED displays then decode and display</div><div>memory locations and the data found in them.</div><div><br /></div><div>A program can be run in "slow motion" and one can</div><div>actually watch the processor access specific memory</div><div>locations to transfer data. In essence it allows one to</div><div>examine, in great detail, the most intimate operations of a</div><div>microcomputer and its programs.<br /></div></div><div><br /></div><div></div>

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