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These are all nice. But at the same time, they're (mostly) representative of the bulk of the 8-bit scene. They only go so far. Ben Eater demonstrates what it
by whartung 5y ago
These are all nice.
But at the same time, they're (mostly) representative of the bulk of the 8-bit scene. They only go so far.
Ben Eater demonstrates what it takes to get a 6502 up on a breadboard (and, with the modern processors and RAM, it's not a whole lot).
In the Z80 world, there's dozens of little Z80 systems with a UART and a flash drive booting CP/M in all sorts of form factors.
But that's where it stops.
There isn't anyone going full boat with a comparable 8-bit video system. The primary question of folks looking at these things, or wanting to do one themselves, is "how do I do video". They all want memory mapped video. Many want color and sprites.
But even skipping color, something akin to a TRS-80 and it's 64x16 screen on a hacked TV set. Or the PET or Apple 40x24 B&W characters. Forget graphics and color and lines. How about "hello world"? I mean, Woz did it with paperclips and shiny gum wrappers, at least so I'm told.
That's where things go off the deep end. It's like there's these simple baby steps to get to a UART, but video? That's...just not in the cards.
Ben Eater did a nice series on getting a VGA video signal using discrete components. It's really informative.
Demonstrably video is very difficult. Apparently anyone that can decipher a tool like KiCad can come up with a 8-Bit processor and a UART. But nobody, anywhere, is doing video.
The few that are doing anything are these retro clones striving to duplicate C-64s, trying to step above the hobby market and break out with a commercial product. But even they struggle.
I just find it curious how this last step seems so out of reach.
The problem may simply be there's nothing to display video on. An 8-bit machine driving even a VGA monitor is asking an awful lot, and I don't know what it takes to convert composite video to run on a modern display, either a VGA or HDMI. I would think if someone came up with THAT circuit, composite in, VGA out, as a "black box", something the board designers could plug in to, like the old RCA boxes we used to use tuned to Channel 3, then maybe that's the breakthrough thats missing from the community. They they could fall back on the old composite circuits from that past.
- zh3 5y agoSurprised to see this as a barrier, it's not hard to generate composite video in hardware/software and there's plenty of composite to VGA/HDMI converters out there (e.g. search Amazon for "composite to HDMI"). I've written plenty of code for PIC micros that generates full-colour PAL/NTSC signals (text and graphics); have to think a bit about how to make it memory-mapped from an 8-bit MCU, some sort of cycle-stealing approach seems feasible (brute-force approach would be to use dual-port RAM or an FPGA, but that doesn't seem in the spirit of 8-bit retro hacking).
- whartung 5y agoYea, I don't know what the barrier is. But there is some barrier. I would think that by now, and this hobby of make 8-bit CPUs is by no means "new", there would be some "oh, Frank did that and has a circuit" so that, at least, everyone makes a stab at using Franks video subsystem. But, nothing.
- zh3 5y agoCould be just that this kind of thing lives on the boundary of electronics, software and precision timing (e.g. for PAL it's necessary to either clock a deterministic MCU at a precise multiple of the colour subcarrier, or use a pile of dedicated logic - lots of chips for TTL or cheat by using an FPGA). To me it just feels 'wrong' to use modern tech to implement a memory-mapped display on a Z80 (I still have a working Nascom 1 [0], which managed to fit a memory-mapped text display into a system with a total 2K of RAM). Happy to discuss further, email is in profile. [0] https://en.wikipedia.org/wiki/Nascom_(computer_kit) https://en.wikipedia.org/wiki/Nascom_(computer_kit)
- jonjacky 5y agoThese kits do include generating the video: https://gigatron.io/ https://gigatron.io/ "... low resolution video had come within reach of our design, without adding chips. This was possible by taking the unconventional step of bit-banging video signals from software, instead of designing a standard video generation circuit. ..." https://basicengine.org/ https://basicengine.org/ "The VS23S010D-L ... is a static RAM chip ... (that) comes with a video controller. ... It comes with 128 kB, some or all of which can be used as a frame buffer ... has a "block move" feature, more commonly known as a blitter. It allows you to copy sections of video memory ... provides a dramatic performance boost in ... text screen scrolling and rendering of tiled backgrounds." http://uzebox.org/wiki/index.php?title=Main_Page http://uzebox.org/wiki/index.php?title=Main_Page - Uzebox - "retro-minimalist homebrew game console. ... video sync generation, tile rendering and music mixing is done realtime by a background task ... easy and fun to assemble and program ... contains only two chips: an ATmega644 and an AD725 RGB-to-NTSC converter." http://www.breatharian.eu/hw/atx80/index_en.html http://www.breatharian.eu/hw/atx80/index_en.html - " VGA and PAL/NTSC video signals are generated by software running along with the BASIC interpreter on the same processor." https://create.arduino.cc/projecthub/michalin70/the-arduino-commodore-64-a7ec45 https://create.arduino.cc/projecthub/michalin70/the-arduino-... - Photos and schematics show the Arduino plugged into a solderless breadboard along with a few passive components to mix the software-generated video signals from the Arduino pins,