{"id":48,"date":"2022-03-28T18:35:03","date_gmt":"2022-03-29T01:35:03","guid":{"rendered":"https:\/\/blogs.oregonstate.edu\/catlistensproutdig88888\/?p=48"},"modified":"2022-04-12T20:27:39","modified_gmt":"2022-04-13T03:27:39","slug":"spring-break-2022","status":"publish","type":"post","link":"https:\/\/blogs.oregonstate.edu\/catlistensproutdig88888\/2022\/03\/28\/spring-break-2022\/","title":{"rendered":"Spring Break 2022"},"content":{"rendered":"

Ah, spring break week, a time to relax. Right? No, not the case. There was finally a week to spend time diving into learning about software-hardware interaction. There was a kit online, found awhile back, and this seemed to be a great time to roll up the sleeves and begin working on wiring, programming, and testing a mini computer.
The kit and some associated video links can be found here<\/a>.<\/p>\n\n\n

Background<\/h3>\n\n\n\n

Since the OSU course 271, intro to computer architecture and assembly, there has been a desire to build a physical model of a computing machine. This desire was one that could not be fulfilled by Arduinos or Micro:bits, it needed to be installing wires and use something other than a GUI with code blocks. The Ben Eater kit for the 6502 processor arrived, the challenge was gladly accepted.<\/p>\n\n\n\n

What is it?<\/h3>\n\n\n\n

Ultimately it is making use of a Western Digital 65c02 processor chip, Western Digital 65c22 versatile interface adapter, common NAND gate (4) chip, ATMEL AT28c256 ROM chip, Hitachi HM62256LP-70 RAM (used as a stack) chip, Hitachi LCD, knob dial for LCD contrast input, resisters, capacitors, 5V input, 1Mhz clock chip, and assorted 20mm insulated wires — on a few breadboards.<\/p>\n\n\n\n

Testing connections was carried out with the MEGA Arduino connection ports, no fanciness with expensive purchase, as Ben states within one of his videos. Less expensive, however over the project, you will dedicate much time to connecting each pin, and in the proper order. Luckily, there is an output on the Serial Monitor. Here you will know if you flipped the pins, as the expected, for example ‘10001111’ would be ‘11110001’. Easy fix, just take the time to look at what this lovely monitor is trying to tell you and update your input probe wiring configuration.<\/p>\n\n\n\n

Programming the ROM was carried out with the EEPROM programmer and this software<\/a>. The assembler used was vasm<\/a>. Currently, it seems all this was easier on a linux system, rather than the starting windows machine.<\/p>\n\n\n\n

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Ben Eater 6502 kit<\/figcaption><\/figure>\n<\/figure>\n\n\n\n

Good Practices<\/h3>\n\n\n\n

Do<\/strong> use some needle nose pliers, wire-strippers (aim for 24\/26), and simple wire-cutters. <\/p>\n\n\n\n

Do<\/strong> double check all connections of the piece you are working on, wires do like to shift, even on the high-quality breadboards.<\/p>\n\n\n\n

Do<\/strong> create index cards with mapping of pins, as the documentation is nice, however the little index cards let you move around and access the information clearly and even build out with a good representation of the chips.<\/p>\n\n\n\n

Do<\/strong> take note of the issues you see, take the scientific approach of only updating one thing, run, compare to last — instead of changing multiple things at once and hoping for the best. \u4e41( \u0361\u00b0\u1a0e \u0361\u00b0)\u310f<\/p>\n\n\n\n

Do<\/strong> take extra care to make the wiring of the clock pin connections as short as possible, this is a help for the proper timing window for some of the pieces to have access to “valid” data chunks, nanoseconds off could affect, other connections do not need as much time investment.<\/p>\n\n\n\n

Do<\/strong> use a single color wire for data and address lines for help in not only understanding, some of the “buss” will carry over to other chips, having different colors helps to reassure the carry over will be correct places if you choose not to look at the pin mapping.<\/p>\n\n\n\n

Do<\/strong> take breaks and work on something else, fresh eyes will be helpful when finding errors, almost like the mind is RAM, and you need to turn it off and come back, you don’t have the previous thoughts, you have something clean to work with.<\/p>\n\n\n\n

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Notecards of the chips (other than NAND and clock)<\/figcaption><\/figure>\n\n\n\n

Programming with a ROM<\/h3>\n\n\n\n

The video walk throughs showed programming the ROM is possible with either python (hardcoding opcodes and variables associated) or assembly language with instructions for the specific 6502 processor documentation. There are probably other languages to use, however these were the ones Ben Eater chose to utilize, of which the project was completed with.<\/p>\n\n\n\n

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left – python of blinking 01010101 then 10101010 for output, right – assembly of 101 scrolling over 8 outputs and looping back<\/figcaption><\/figure>\n\n\n\n

For the python code above, the goal was to see the optical illusion of blinking LEDs, which can be created by looping ‘01010101’ and ‘10101010’. Below you will find a video demonstration after the upload to the ROM chip and some LEDs are installed. You might notice the strange LED above the grouped LEDs, this is another module of Ben Eater’s kits, the clock module kit. It allows you to have a less-professional (in terms of clean signal transition to high\/low) variable speed and for debugging\/seeing each cycle on the Arduino MEGA — a push button for creating a “clock cycle”. This was useful to physically see the cycle needs for some of the instructions outlined within the 6502 processor documentation.<\/p>\n\n\n\n