Search found 181 matches

by ThomH
Sun Jan 01, 2017 11:54 pm
Forum: Tape and floppy disk converters
Topic: Track reading (Sedoric / FDC)
Replies: 52
Views: 38969

Re: Track reading (Sedoric / FDC)

Probably far too late to be of any help, but... The surface of a floppy is just a bunch of oriented magnetic regions. A 1 bit is flagged anywhere that a region with magnetism running in one direction transitions into a region with magnetism pointing in the other. Different drives run at slightly dif...
by ThomH
Sun Jan 01, 2017 9:15 pm
Forum: Emulators
Topic: Clock Signal — an Oric emulator for macOS and Linux
Replies: 103
Views: 54611

Re: Yet Another

I think there were a few protected software, for instance XL-DOS is a well known one. IIRC a few games / utilities were too, but I forgot which. About Read Track, maybe this topic will bring some (depressing) information! I'm on my phone so possibly skimming more than is respectful to the original ...
by ThomH
Sun Jan 01, 2017 6:27 pm
Forum: Emulators
Topic: Clock Signal — an Oric emulator for macOS and Linux
Replies: 103
Views: 54611

Re: Yet Another

[*] I've yet to implement the WD177x type 3 commands — read track, write track and read address, or most of the type 4s. So all that immediately gains is write sector. There's a whole bunch of work underneath to make that work as I insist on using a reasonably accurate model of drive mechanics and ...
by ThomH
Sat Dec 31, 2016 10:31 pm
Forum: Emulators
Topic: Clock Signal — an Oric emulator for macOS and Linux
Replies: 103
Views: 54611

Re: Yet Another

I've made a further release . Highlights are: disks are now writeable; original colour ROM values are used for composite colour generation. Caveats are: I've yet to implement the WD177x type 3 commands — read track, write track and read address, or most of the type 4s. So all that immediately gains ...
by ThomH
Wed Dec 28, 2016 8:55 pm
Forum: Tape and floppy disk converters
Topic: Tape Header Format
Replies: 9
Views: 15122

Re: Tape Header Format

I've thrown this onto the wiki, which I think matches the exposition given above plus some detail on the actual waveform and a brief mention of the hardware/software implementation. Hopefully it's accurate but if not then, well, it's a wiki. So easy to fix.
by ThomH
Tue Dec 27, 2016 6:04 pm
Forum: Games
Topic: Development of Blake's 7 (was OASIS development)
Replies: 600
Views: 390174

Re: OASIS development

If Chema was planning to release commercial versions of his game, duplicating the floppies himself, that would definitely be the way to go. On the other hand, if all he wants is to make it easier for people to play the game on as many machines as possible, and make sure it can be easily copied, no ...
by ThomH
Tue Dec 20, 2016 7:14 pm
Forum: Games
Topic: Development of Blake's 7 (was OASIS development)
Replies: 600
Views: 390174

Re: OASIS development

Possibly a tangent but if what we're talking about is a read-only format and total storage is an issue, why not dispense with sectors after the first track? Though you'd probably then need to avoid use of byte values above F4 if you want to be able to write the thing on Oric hardware and/or store re...
by ThomH
Fri Dec 09, 2016 5:08 pm
Forum: Technical questions
Topic: Composite video generation
Replies: 7
Views: 9245

Re: Composite video generation

Impressive! This is too complex for me, I admit; however I'd like to point out that there is a variable resistor which lets the user modify the color "intensity" from b/w to something which was completely distorted but very bright :) I am quite sure you are aware of it, but the color output of the ...
by ThomH
Fri Dec 09, 2016 1:59 pm
Forum: Technical questions
Topic: Composite video generation
Replies: 7
Views: 9245

Re: Composite video generation

Also from the repair guide, I was off about that phase counter. It's two independent signals in quadrature, not a direct counter. So it counts 00, 01, 11, 10. Close though. I still have a phase error in detecting the colour burst but here's the very first 'working' output based on throwing direct co...
by ThomH
Thu Dec 08, 2016 9:13 pm
Forum: Technical questions
Topic: Composite video generation
Replies: 7
Views: 9245

Re: Composite video generation

Seemingly confirmed. Indexing into that ROM is: apRG Bscc a = even or odd line; increments every sync p = is in back porch; stays high for a while after sync to effect the colour burst RGB = the colour channels s = sync, active high; cc = phase within the colour cycle, increments close to 1135 times...
by ThomH
Thu Dec 08, 2016 6:59 pm
Forum: Technical questions
Topic: Composite video generation
Replies: 7
Views: 9245

Re: Composite video generation

iss wrote:It's already in the old posts ;).
Oh, with an 'N'! That looked like a smudge on the photo I grabbed.

That's really cool. I'll be able to test my guesses about the meanings of the other lines and report back. I wish I were better at electronics.
by ThomH
Thu Dec 08, 2016 5:26 pm
Forum: Emulators
Topic: Clock Signal — an Oric emulator for macOS and Linux
Replies: 103
Views: 54611

Re: Yet Another

I've hatched off a different thread to enquire further about video generation. It looks like there's a lookup ROM involved and fairly limited precision on the colour subcarrier but I don't have a real machine or any idea how I would dump the thing even if I did so possibly that's a dead end. Being t...
by ThomH
Thu Dec 08, 2016 5:21 pm
Forum: Technical questions
Topic: Composite video generation
Replies: 7
Views: 9245

Composite video generation

I'm a circuit-reading dunce. Having opened with that, I was looking at the Oric schematic to try to learn a bit more about how composite video is generated. The relevant area seems to be along the top of the schematic, mostly to the right. First point of great interest: there's a 256x4 PROM involved...
by ThomH
Wed Dec 07, 2016 10:01 pm
Forum: Emulators
Topic: Clock Signal — an Oric emulator for macOS and Linux
Replies: 103
Views: 54611

Re: Yet Another

Separately, while looking into the "colours aren't right" issue, I've been grabbing some original television images from Youtube. It seems to vary from title to title but looking at the Manic Miner and Doggy as attached, there seems to be quite a lot of noise in some areas. If it's something the ori...
by ThomH
Wed Dec 07, 2016 6:00 pm
Forum: Technical questions
Topic: Does anybody have the WD1793 data sheet?
Replies: 6
Views: 7293

Re: Does anybody have the WD1793 data sheet?

Thanks! Those helped a lot. I won't bore you with the full litany of errors one could make by taking that "the WD1773 is 1793 compatible" statement too strictly but the absence of head loading logic is a lot of it. For the Microdisc, I settled upon signalling HLT 7,653,333/8,000,000ths of a second a...