[JMR202001151915: Backup]
Chapter 1: Homecoming Dance
Chapter 2: Christmas Present -- Micro Chroma 68
For Christmas, my brother Dennis and his wife Denise came up from Austin where Denny worked for Motorola as a microprocessor test engineer. My sister Louise was in Germany with Bruce and their kids, but Giselle was at home, and Sherise and RebeccaLee came in from BYU. Five of the six siblings, one in-law, and two nephews.
I had fun being monkey bars and bucking bronco for my nephews, and talking about my mission with my siblings. Kids always seemed to have fun climbing on me.
Denny and I found some time to talk microprocessors, especially news about the 6809 (the partially 16 bit redesign of the 6800), and about the 68000 (the 16 bit/partially 32 bit riff on filling in the deficiencies of the 6800 inherited from Motorola's early model 680 minicomputer). He had some technical notes for the CPUs and the peripherals, and I took a little time to scan through them.
Christmas morning, I had an unexpected flat present. Unwrapping it, I found a printed circuit board, manuals, and integrated circuits for a microprocessor prototyping kit, and a small pile of related spec sheets and technical datasheets Denny hadn't given me the night before, to avoid spoiling the surprise.
"Whaddaya think?" he grinned.
"Uhm, ..." I spread the kit out and looked at the manual. "Micro Chroma 68. Engineering prototyping kit for the 6808. Interesting." To say the least.
"Yep. You can put a keyboard on it and save programs and date to tape. Hang an adapter on it to plug into the TV for video output. I snagged one of these for me, too. I even snagged us both a BASIC ROM."
"BASIC? No assembler?"
"Assembler? You sure you wanna mess with that?"
"BASIC in ROM may make for a good programmable calculator, but it just feels clunky. All those gotos."
"Gotos are not evil."
"Just clunky."
Denny just grinned lopsidedly and wiggled his ears.
He lifted a bag of something that looked like really short, fat pins.
"What's that?"
"For the ROM socket. They fit in the through-holes and turn the board itself into a socket. Very low profile, and you can even solder point-to-point wiring on them."
"So I can plug something else in if I want. Great! I'll be using assembly language in my microprocessors class. The class is using the 8080, but I got permission to use the 6800, if I could get the kit for it."
"Well, you should go ahead and learn the 8080, too." (In the real world, we discussed whether learning one CPU well would ruin a person for another, without having enough experience to come to a correct conclusion.)
"I plan to." (I was hedging.)
"The monitor ROM has an in-memory disassembler."
"Monitor ROM?" I dug into the manual and found that section. "Oh, yeah. In the multifunction chip. This is good. Definitely be useful for this class."
"I snagged you most of the chips. The rest of the parts you can get at Radio Shack."
Semiconductors are made on wafers, and the wafers are sliced up into chips of wafers, which are then put into packages. Back then, the packages often looked like centipedes or other multi-legged creatures. The electronic connection leads looked like legs coming out of the little plastic case body. Now the packages themselves are usually flat and look like what US-Americans usually call chips.
"Didn't this cost a lot?"
"Engineer incentive program. One part bad and they toss out the whole batch it was in. Engineers are allowed to borrow test equipment after work and look for good parts from the recycle barrel, and use them for personal projects. The mainboard was available for cheap, too."
"So we're going to have to get keyboards."
"True. There's a surplus parts place in Austin, if you can't find keyboards here."
"Mom ..."
She was sitting nearby, talking with Denise and my sisters.
"You want to go to Austin, don't you? I can run the paper route while you go." Mom gave me her own encouragingly lopsided smile.
"Where's my soldering iron? Is it complete enough we can get video out before you head back to Austin?"
"Let's see if it is."
It was, almost.
I actually didn't get the iron out immediately, there was family business first, and board games to play, too. And I had to go to Radio Shack the next day to get some resisters, switches, connectors, a transformer, and a voltage regulator for the power supply.
But by the time Denny and Denise and their kids headed back to Austin we had video output from the monitor ROM on both our boards, waiting for input from a keyboard:
VDG DEBUG SYSTEM TV-BUG VER 1.2
MOTOROLA -- AUSTIN, TEXAS
TVBUG
And a flashing cursor after the TVBUG prompt.
"Well, it comes up this far."
"Test the monitor ROM?"
"No keyboard."
"Bob Burns said you could short the keyboard matrix pads to get keypresses."
"No way. Let's look at the matrix diagram."
There was no matrix diagram. We spent some time puzzling over the circuit board diagram.
"It's expecting a decoded keyboard, pre-baked 7-bit ASCII codes and a strobe. Trying to figure out how to short that's gonna bend my brain tonight."
"Gotta be a way."
"We can short the cursor keys, maybe."
We tried that, and we got the cursor to move.
"Success."
"Skin, bro."
I slapped his outstretched hand and we unplugged it and rejoined the family.
"No color."
"Black and white TV is just fine. You've got a color TV at your place."
During my teenage years, the black and white TV I bought with newspaper route money was the only TV in the house.
"Do you need a color TV?" Dad asked.
"No. There are other things I need first, like an oscilloscope."
"Oh! Silly scope! Sounds like TV to me."
We all chuckled at Dad's pun. We knew we couldn't discourage him, so we just enjoyed it.
A few technical details of the Micro Chroma 68, for those who are interested:
The principle integrated circuits for the computer were
- Central Processor Unit (CPU): Motorola 6802, a 6800 with built-in
clock circuit. The 6802 had 128 bytes of RAM, too. The 6808, the chip
that was actually specified, was a 6802 with RAM that was not in spec.
Either would work here.
(But not the 68HC08, a different, later Motorola microcontroller system-on-a-chip (SOC) with a single 8-bit accumulator and a lot of optional RAM/ROM/ports/timers/etc.)
- Video Display Generator (VDG): Motorola 6847, capable of displaying
16 rows of 32 column text, or 256 (horizontal) by 192 (vertical)
monochrome resolution on the analog TVs of the time. Had limited color
output capabilities in this configuration.
Note that this was the VDG used in the Tandy/Radio Shack Color Computer, which figures somewhat prominently later on in the story.
- ROM/IO/Timer: Motorola 6846, a multifunction part containing the
monitor program in ROM, 8 bits of parallel I/O plus two bits of
handshake, and a 16 bit timer/counter.
(But they didn't call it a RIOT. That was the MOS Technologies 6502 family 6532, which had random access memory (RAM) instead of read-only memory (ROM).)
The Micro Chroma 68 controlled the Video Display Generator graphics modes with this port.
- a 6821 parallel interface adapter, with two 8 bit ports plus two bits of handshake for each. This was mostly for the keyboard.
The monitor ROM code uses this part as the keyboard interface port.
- a 6850 ACIA asynchronous serial communications interface adapter for
a serial port that the monitor ROM used as a slow cassette tape
interface.
It could also be used, with very little circuit modification, for serial communications such as RS-232C.
- 30 static 2114 RAMs, 1024 by 4 bits each, for 8 kilobytes (8K) of
program/data RAM, 1K of system RAM (as used by the monitor), and 6K of
video RAM.
In case you are curious, Motorola did not revise the ROM or circuit to make a 6802's internal 128 bytes of RAM available.
In addition, there was a breadboard area at the bottom of
the board, for adding arbitrary circuits of the user's choice, and a
card-edge connector that could, with appropriate buffers, plug into a
Motorola Exorciser (TM) bus. (Yes, engineers love arcane puns, and
sometimes not-so-arcane puns.)
"Hey, how about a round of Pit?" It was Dad's suggestion.
And we all enjoyed Pit, so Giselle got out the Pit deck and we played a few games.
Chapter 3: School
[Backed up at https://joel-rees-economics.blogspot.com/2020/01/bk-33209-christmas-present-micro-chroma-68.html.]
[JMR202001151915: End.]
[JMR202001091914: Backup]
Chapter 2: Christmas Present -- Micro Chroma 68
For Christmas, my brother Dennis and his wife Denise came up from Austin where Denny worked for Motorola as a microprocessor test engineer. My sister Louise was in Germany with Bruce and their kids, but Giselle was at home, and Sherise and RebeccaLee came in from BYU.I had fun being monkey bars and bucking bronco for my nephews, and talking about my mission with my siblings. Kids always seemed to have fun climbing on me.
Denny and I found some time to talk microprocessors.
Christmas morning, I had an unexpected flat present. Unwrapping it, I found a printed circuit board, manuals, and integrated circuits for a microprocessor prototyping kit.
"Whaddaya think?" Denny grinned.
"Uhm, ..." I spread the kit out and looked at the manual. "Micro Chroma 68. Engineering prototyping kit. Interesting." To say the least.
"Yep. You can put a keyboard on it and save programs and date to tape. Hang an adapter on it to plug into the TV for video output. I snagged one of these for me, too. I even snagged us both a BASIC ROM."
"BASIC? No assembler?"
"Assembler? You don't wanna do that. Too low level."
"For my class."
"You should go ahead and learn the 8080, too."
"I plan to. Besides, BASIC in ROM may make for a good programmable calculator, but it just feels clunky. All those gotos."
"Gotos are not evil."
"Just clunky. So we're going to have to get keyboards."
"True. There's a surplus parts place in Austin, if you can't find keyboards here."
"Mom ..."
"I can run the paper route while you go to Austin." Mom give me an encouragingly lopsided smile.
"Where's my soldering iron? Is it complete enough we can get video out before you head back to Austin?"
"Let's see if it is."
It was.
I actually didn't get the iron out immediately, there was family business first, and board games to play, too. And I had to go to Radio Shack the next day to get some resisters, switches, connectors, and a transformer for the power supply.
But by the time Denny and Den and their kids headed back to Austin we had video output from the monitor ROM, waiting for input from a keyboard:
VDG DEBUG SYSTEM TV-BUG VER 1.2
MOTOROLA -- AUSTIN, TEXAS
TVBUG
And a flashing cursor after the TVBUG prompt.
"Well, it comes up this far."
"Test the monitor ROM?"
"No keyboard."
"Bob Burns said you could short the keyboard matrix pads to get keys."
"No way. Let's look at the matrix diagram."
There was no matrix diagram. We spent some time puzzling over the circuit board diagram.
"It's expecting a decoded keyboard. Trying to figure out how to short that's gonna bend my brain."
"Gotta be a way."
"We can short the cursor keys, maybe."
We tried that, and we got the cursor to move.
"Success."
"Skin, bro."
I slapped his outstretched hand and we went back to the kitchen to rejoin the family.
"No color."
"Black and white TV is just fine."
During my teenage years, the black and white TV I bought with newspaper route money was the only TV in the house.
A few technical details of the Micro Chroma 68, for those who are interested:
The principle integrated circuits for the computer were
- Central Processor Unit (CPU): Motorola 6808/6802, a 6800 with
built-in clock circuit, 128 bytes of RAM in 6802. Either the 6802 or the
6808 would work here.
(But not the 68HC08, a different Motorola microcontroller system-on-a-chip (SOC) with a single 8-bit accumulator and a lot of optional RAM/ROM/ports/timers/etc.)
- Video Display Generator (VDG): Motorola 6847, capable of displaying
16 rows of 32 column text, or 256 (horizontal) by 192 (vertical)
monochrome resolution on the analog TVs of the time. Had limited color
output capabilities in this configuration.
Note that this was the VDG used in the Tandy/Radio Shack Color Computer, which will figure prominently in this story.
- ROM/IO/Timer: Motorola 6846, a multifunction part containing the
monitor program in ROM, 8 bits of parallel I/O plus two bits of
handshake, and a 16 bit timer counter.
(But they didn't call it a RIOT. That was the MOS 6502 family 6532, which had random access memory (RAM) instead of read-only memory (ROM).)
The Micro Chroma 68 controls the Video Display Generator modes with this port.
- a 6821 parallel interface adapter, with two 8 bit ports plus two bits of handshake for each.
The monitor ROM code uses this part as the keyboard interface port.
- a 6850 ACIA asynchronous serial communications interface adapter for
a serial port that the monitor ROM used as a slow cassette tape
interface.
It could also be used, with very little circuit modification, for serial communications such as RS-232C.
- 30 static 2114 RAMs, 1024 by 4 bits each, for 8 kilobytes (8K) of
program/data RAM, 1K of system RAM (as used by the monitor), and 6K of
video RAM.
In case you are curious, Motorola did not revise the ROM or circuit to make a 6802's internal 128 bytes of RAM available.
In addition, there was a breadboard area at the bottom of the board, for adding arbitrary circuits of the user's choice, and a card-edge connector that could, with appropriate buffers, plug into a Motorola Exorciser (TM) bus. (Engineers love arcane puns, and sometimes not-so-arcane puns.)
Chapter 3: School
[Backed up at .]
[JMR202001091914: End.]
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