A Reptile Dysfunction 4h ago

Tonight, instead of doing another bring-up stream, I focused on a tedious but important task on the MiniDragon: identifying and labeling the MSB/LSB on each bus connector. And by that, I mean the most significant bit, and least significant bit. Most of the components are bit-order agnostic. As long as you output the same order you input, they'll work. But, now that everything is piped together, there needs to be an agreed-upon bit order! So, I did that!

I do have some old physical layout documentation that dictated my conventions at the time, and I've verified those are upheld. But, the labels are way easier to read and see.

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Show threadA Reptile Dysfunction 11h ago

Alright. I excitedly filmed a demonstration of the adder circuit integrated with the ALU and working properly. Please pardon my math mistake partially through where I got super confused about 15+5 coming in at 4. I explain in the video description what's going on there. Please check it out, this is about 5 years of work on and off to get here :3

https://www.youtube.com/watch?v=hHq58udeiqo

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MiniDragon ALU Adder Circuit Integration

YouTube
A Reptile Dysfunction 11h ago

dfghdoihgdoifghdifogh the ALU is WORKING.

#MiniDragon

A Reptile Dysfunction 4d ago

Brought up two more 2-bit adder boards tonight on stream. After testing them individually I tied them to the existing two for shiggles. Behold, a 8.5" by 7" stack of boards that adds two 8 bit numbers with carry in and carry out. I got 4 more to bring up at some other point to have a functioning 16 bit adder, which I need in order to do indirect addressing and manipulate the instruction pointer and stack pointers (relative jumps, moving the stack pointer forward or reverse by an immediate or the A register, etc) and have arbitrary access to all 64K of memory.

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A Reptile Dysfunction 5d ago

tonight's meditative assembly was a bunch of distributor boards that i need for future panel layouts. the only components on any of these that aren't just pin headers are a bunch of capacitors on the power distributor boards. still, they make wiring boards to each other much easier and give things a bit of polish.

#MiniDragon

Emily Hare5d ago
I recently made a tiny collection of dragons - so i'm trying out doing a print of them collected together. #dragons #dragonart #minidragon #watercolour #painting #prints get yours here: buff.ly/rUmKeem
Bluesky

Bluesky Social
Show threadA Reptile Dysfunction Apr 8

And then there were 14!

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A Reptile Dysfunction Apr 7

i guess if i need to bring up one of these bus converter boards again, i might as well replace the other one that i needed to patch around a PCB trace issue with a jumper, as well as do two more for the as-of-yet-to-be-built U and V registers. so, that's 4 boards to bring up in total, again.

#MiniDragon

A Reptile Dysfunction Apr 7

i needed the quick win of finishing these 12 boards. didn't get it, one of the boards has a dead short between VCC and GND. i have exactly zero components that bridge VCC to GND directly aside from the decoupling capacitor which i removed and verified. chances of somewhere in the chain having both an internal short in a transistor coupled with a bad resistor are effectively zero. checked everything I could see, but this suggests an actual PCB error. gave up on it, will have to bring another one up from scratch at some point. bleh 

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Show threadA Reptile Dysfunction Apr 3

okay so i was sticking with TTL-compatible CMOS in PDIP format for the stuff on the memory bus of MiniDragon to try to be somewhat period-accurate-ish. i know that if we're in the timeframe of true discrete transistor computers that the hardware for a UART/RS-232 would have been designed from scratch too, and that integrated circuits would have been massively too expensive. but also, eh, this is already an anachronism since i was planning on pairing it with a vt-100 which came out in 1979 by which point NOBODY was designing transistor CPUs.

i guess i gotta think about my design constraints a bit. there's plenty of QFP and similar. or i could go with an older design that's EOL in order to get a PDIP design (such as i8250 or SCN 2681) but eBaying chips in 2025 is like "please scam me china 🥺"

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