Chapter 11.0: Headwinds -- IBM
Chapter 11.1: Headwinds -- 68701
I looked up at the tap at the open door.
"Pat. Hi. What brings you to the Electrical and Electronics Building? Slumming?"
"The profs were talking about your success yesterday with raw I/O. We wanted to see for ourselves."
"We? Ah, Mike. George. Hi guys."
"Yo."
"Hey."
"Well, come in and join the crowd."
They came into the electronics lab and joined the group of students gathered around the lab table where my lab partners, Jeff and Mark, were sitting in front of the Micro Chroma 68.
Dr. Brown hadn't wanted to take more class time, so he had suggested that I take time after class to let interested students watch me reproduce my results from the day before. I could chase them off after, if they distracted my progress too much.
Jeff and Mark were by this time familiar with the Micro Chroma 68, and had volunteered to help as soon as they saw me coming in with the computer again.
We had the video output connected through a splitter to both my TV and the lab's large-screen TV so the other students could see what was showing on my TV screen.
I walked Jeff and Mark through my work of the day before, letting them operate the computer and set up the circuits from my notes while I drew diagrams on the chalkboard and explained and answered questions about the circuits and the timing issues as I understood them, starting with bit-banging and working up to the FM encoding. Dr. Brown added comments when he thought they were necessary.
Part way through the demonstration, I noticed Julia watching from the doorway. When I raised my hand in a wave to her, Pat turned and looked, and something passed between them that I didn't follow. Julia entered the room and sat in my seat at the lab table.
When we'd finished demonstrating recording and playing back test data in FM, Jeff looked up from the screen. "Is there some way we can look at a track before it gets written?"
I looked at Dr. Brown and he just grinned back at me. So I thought for a moment. I reached over to the breadboard and removed the FM decode circuit.
"We haven't written anything to track 30, yet, Jeff. Bump the heads up to track thirty."
He typed in the commands that moved the head.
"Run the read routine and let's look at the read buffer."
He did so, and we watched him list patches of mostly zeroes, of short repeating sequences, and of random numbers.
"Does it look pretty random?"
Everyone thought it did.
"I think if we looked hard enough, we should find twelve cycles of line noise in there. Should we take the time?"
Julia frowned. "I hate to ask a stupid question, but what's line noise?"
Mike said, "Thank you for asking."
I gave her a nod I hoped was reassuring. "There are no stupid questions, right, Dr. Brown?"
"Except the ones you don't ask." He nodded sagely.
Dr. Brown's students all nodded, too. They'd heard it before.
"The sixty Hertz hum in the power line," Mark answered for me.
"Sorry?"
Jerry held up a power plug. "Wall power. If I'm following this right, 300 revolutions per minute means that a track takes a fifth of a second to read." He looked at me for confirmation.
"Right."
"And a fifth of a second," he continued, "is time for twelve alternating current cycles, from plus 120 volts RMS to minus 120 volts RMS and back again."
Julia tilted her head. "Is that the hum my stereo makes when I turn the volume way up and nothing is playing?"
"Yep."
"Oh, I get it!" Greg laughed. "Thank you for asking that question."
Several other students murmured agreement.
Winston shook his head. "It sounds to me like an exercise in advanced statistics."
Nobody seemed anxious to spend time on the analysis.
"Oh, well," I said, "I'll just have to try this in the statistics class, I guess."
"So what about yesterday's data?" Mark asked. "Is it still there?"
"It should be. Jeff, can you bump the heads back down to track 5 and run the read routine?"
He did so, and listed the buffer again.
"Mathematical sequences," Julia commented in a low voice. Then Giselle's and Julia's names showed up.
"Hey, hey, hey, who are Giselle and Julia?" Mike wisecracked.
"Giselle is Joe's sister," Julia said with barbs in her voice.
"Yep." My eyes met Julia's.
She shook her head, barely perceptibly.
"My sister. Shall we type in everyone's names, and write them to track 30?"
There was some laughter, but Jeff started editing the buffer contents, grinning as he worked. He added Julia's and Giselle's names without prompting, and asked for Pat, Mike, and George's names, to add, too. He ran the write routine, cleared the buffer, and then ran the read routine, and it read back perfectly.
Julia clapped a slow clap, and others joined in, with some cheering and laughter.
"I stlll don't really follow what you're doing," she said when the noise quieted down, "and your presentation could use some work, but now I believe you when you say it puts stuff on the disk."
"That wasn't the presentation for the board of directors, thank you." I chuckled, and Julia laughed. Some of the other students laughed nervously, and Dr. Brown chuckled.
"Okay, everybody. I now need to dive deep into some arcane math, so I can use these drives to share data with other computers. The fun stuff is over for the day, unless you're into really arcane math."
Mark and Jeff exchanged glances.
"So have you figured out yet how we can get computers like these?" Mark asked.
"There is Radio Shack's Color Computer, as I've mentioned before."
Jeff shook his head. "We want to build our own."
"I can ask Denny if Motorola has any more of the Micro Chroma 68 PC boards that they would be willing to sell to students, but wouldn't you rather build something with a more modern processor?"
"Waiting for you to build something better has its own costs," Jeff groused. "This obviously works now."
There were murmurs of agreement.
"I'll ask. But I really think we could design something cool if we worked together."
There were murmurs of approval.
Jeff was not to be satisfied. "But when?"
"What do you think, Dr. Brown?"
Dr. Brown grinned. "I'm not going to tell anyone what they can't do with their own time."
"Okay." I rubbed my forehead and checked my watch. "But I want everyone to understand a few things. The reason I am using Motorola parts is that my brother Denny can get me lots of those. He can't do that for non-family, so if you decide to build these with me, you'll be buying the parts yourselves."
Jerry gave two thumbs up. "No problems here."
Winston added, "All the more reason to get parts ordered now."
"And I'm not promising anything, especially if we start now. Don't blame me if you decide you wanted a 6502 or Z-80 or 1802."
"No problem."
"We've got this."
"What's a Z-80 got to do with it?"
"In fact," I added, "no guarantees of anything. Strictly participate at your own risk."
"If you're saying we're going to see something today, I'm definitely in," Mark said, to general nods and murmurs of agreement.
"See something?"
"A parts list would be good."
"Okay, what I have in mind for myself is replicating this box using the 6801, then the 6809, and then the 68000. But I'm sure most of you don't want to end up with three or four computers."
Jennifer shook her head. "Let us decide when to get off the train?"
I thought for a full minute before proceeding with a sigh. "How many of you want trainers like the 8080 trainers that the lab has?"
All the electronics students raised their hands.
I looked at Dr. Brown.
He grinned back. "What do you suggest?"
I tilted my head left and right, stretching the muscles in my neck.
"I think I want to start with an EPROM 6805, just enough to decode a keypad and a keyboard and send address and data to seven segment displays. A 6805 is powerful enough to build a calculator with, but it will quickly become uninteresting if you want to hang a display on it, and run a full OS and programming languages."
I went to the chalkboard and erased a panel while I thought.
"Starting with a 6801 will be one step quicker, but it will cost more money."
Winston spoke up. "Time is money for me."
"Okay." I drew a square for the CPU. "68701 here." I wrote the number in.
"Should I take notes?" Julia offered, to my surprise.
"If you would, sure. Thanks."
She got a pen and a pad of paper out of her purse. "68 .. 68701, right?" She copied what I was drawing.
"Right. 68701. I'll probably have to find a source for that. The keyboard and keypad don't need exact timing so we can use an RC circuit for the clock, and the resistors and capacitors are probably in our kits, or can be got at Radio Shack." I sketched those in. "Latches for de-multiplexing address and data can found at Radio Shack, too. Don't need full 6821s for the ports, so we can use latches for those, too. We can get those are Radio Shack, so we can talk about specifics next week." I drew them in.
"Hexadecimal keypad and six, no, seven seven-segment LED displays." And I drew those in. "We'll have to find part numbers for displays that can be persuaded to show hexadecimal codes. We may be able to find those at Radio Shack, or maybe not. The 7400 series logic to glue it all together can definitely be found there."
I continued filling in blanks, and most of the students had paper out and were copying the diagrams. Julia was checking the notes she was taking for me with Mark.
"Boy, I wish you guys had this much motivation in my classes." Dr. Brown deadpanned.
Laughter erupted. I waited until it subsided a bit.
"It's because of your classes that we can follow what this genius is doing."
"Winston, we are all geniuses."
"Whatever."
More laughter.
"Yeah. Okay, this should be enough for a trainer that can be attached to a breadboard, like the 8080 trainers, and I'll find a source for the monitor program. And then we can turn it into a keyboard controller. Let's get together after class next week to make real schematics. Anyway, what you should be doing over the weekend is making your own version of the diagrams, and looking around in stores, in magazines, and in the library or whatever, information and for sources for buying the parts. And we can share what we find next week. Probably want to hold off actually ordering anything until we've had some more time to plan things out."
George looked at Mike and Pat. "I think I'm in on this."
Mike responded with, "Me, too. Pat?"
Pat tilted her head. "I'm thinking about it. Julia, what do you think?"
"I'm here for my own reasons."
There were scattered chuckles.
Julia's and my eyes met, and she didn't add anything.
Dr. Brown cleared his throat. "Was anyone hoping to build something with the 68000?"
Several hands came up.
"For what it's worth, starting small is the best way. I do not plan on approving the 68000 for the microprocessors class. Not this time around. It's a bit too powerful and too expensive, and looks like a nice big rabbit hole to dive into. When the cost comes down, I'll rethink that, but for now, I very much approve of the decision to start with the 6801."
He paused for thought. "Look ahead, be sure you do your own work, take notes, make diagrams. Leave something you can show me, and we can definitely use this in the Microprocessors class."
More murmurs of enthusiasm.
I sighed. "Okay, I've got to get these disks running. Thanks for coming to encourage me, and let's get together again next week."
Most of the students stopped on their way out to say thanks. Pat, Julia, Mike, and George left together.
Dr. Brown hummed some country and western tune. "I've been talking with the school board."
I gave him a sharp look.
"You bet I have. I have permission, if there's interest, to turn this project of yours into a multi-semester project class, if things go well."
"Now I really feel pressure." I chuckled wryly.
He just grinned.
I still had time, before I had to go home to deliver newspapers, to put an hour into working out math, turning the math into circuitry, and testing my results with the oscilloscope.
Chapter 11.2: Headwinds -- Religion
[Backed up at https://joel-rees-economics.blogspot.com/2020/03/bk-33209-headwinds-68701.html.]
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