Search found 85 matches

by mikeb
Mon Aug 12, 2019 5:16 pm
Forum: Hardware hacks and extensions
Topic: Printer cable: Oric to DB36?
Replies: 10
Views: 1439

Re: Printer cable: Oric to DB36?

I'm not sure if DB36 is the right description -- I think of DB as being the DB-9/15/25 "D-sub" range (like for mice, joystick, serial ports) A proper Centronics was usually an Amphenol 36-way (2 row) connector. Like the IEEE488/GPIB/HPIB (24 pin?) but obviously bigger. See: https://en.wikipedia.org/...
by mikeb
Sat Aug 10, 2019 7:44 pm
Forum: Technical questions
Topic: Oric-1 Repair
Replies: 44
Views: 3284

Re: Oric-1 Repair

I've got an Atmos that boots but it is rather reluctant. It can take 3 or four times plugging in the power supply. I've swapped the C8 and C21 with no change. The chips are mostly socketed so I've swapped 6502, 6522 and RAM and it is still struggling. When it powers up (but fails to boot), what hap...
by mikeb
Tue Jul 23, 2019 5:48 pm
Forum: Technical questions
Topic: A possible software alternative to Vsync?
Replies: 47
Views: 22572

Re: A possible software alternative to Vsync?

Simple. Real PAL television sends a 312 line field followed by a 313 line field (interlacing). Neither 312 nor 313: Split the difference and it'll be fine: For real PAL it's actually 312 and a HALF lines in each field, which is why the second lot of 312.5 land "between" the first set (to interlace)...
by mikeb
Fri Jul 19, 2019 5:58 pm
Forum: Painting tricks
Topic: LORES: different between ROM 1.0 and ROM1.1?
Replies: 3
Views: 670

Re: LORES: different between ROM 1.0 and ROM1.1?

No idea how it was fixed, $F263 is the highest address that "Rambling In The ROM" got to in OUM, so that would be where I would look for details. There must be a subtle difference between the routines (a stray ROL or something) hidden in there that fixes it. Edit to add: I just compared Leycester Wh...
by mikeb
Fri Jul 19, 2019 5:54 pm
Forum: Technical questions
Topic: What is the purpose of this resistor ?
Replies: 2
Views: 188

Re: What is the purpose of this resistor ?

Secret purpose. Gateway to Narnia. Do not mess with it :) It's been sat there looking out-of-place, and yet completely innocent, all these years, and its purpose is to stop that video "output" line accidentally floating up to +5v. Spoiler Alert: This pin is also an input, but its not documented, unt...
by mikeb
Thu Jul 18, 2019 5:57 pm
Forum: Painting tricks
Topic: LORES: different between ROM 1.0 and ROM1.1?
Replies: 3
Views: 670

Re: LORES: different between ROM 1.0 and ROM1.1?

Yes, this is a long standing feature :) The character cells are supposed to be an equal 2 x 3 grid for teletext/viewdata blocks For Oric this means 3 pixels left, 3 pixels right, as there are only 6 bits in a character that become visible pixels (the other 2 bits are for attributes etc.) xx 000 000 ...
by mikeb
Wed Jul 10, 2019 5:03 pm
Forum: Technical questions
Topic: Telestrat failure?
Replies: 22
Views: 1820

Re: Telestrat failure?

Yes, well, obviously the dog is going to come off worse for that encounter ... ever trod on a DIP IC? Barefoot? I can't see the dog enjoying it on the way in. On the way out will be worse ... Meanwhile, another "risk" -- I found two spare Oric V1.1 Basic ROMs and ULAs, carefully preserved in antista...
by mikeb
Mon Jun 24, 2019 4:48 pm
Forum: Hardware hacks and extensions
Topic: Atmos with a Slice of Raspberry Pi
Replies: 9
Views: 827

Re: Atmos with a Slice of Raspberry Pi

If you want reasonably bi-directional, capable of handling various logic levels and analogue too, you could look at CMOS bilateral switches (e,g, 4066) a.k.a transmission gates. You may need to roll your own "double throw" by using two on-off switches, and negating the logic of on compared to the ot...
by mikeb
Thu Jun 20, 2019 4:46 pm
Forum: Technical questions
Topic: Telestrat failure?
Replies: 22
Views: 1820

Re: Telestrat failure?

Sounds like a cool project, but also -- I wonder if erasing these chips can be "optimized" using that technique, like the reverse of the programming strategy I mentioned: Fast Erase: Put UVEPROM under UV light and read it continuously until it returns all 1's, time how long that takes, then give it ...
by mikeb
Wed Jun 19, 2019 5:04 pm
Forum: Technical questions
Topic: Telestrat failure?
Replies: 22
Views: 1820

Re: Telestrat failure?

Depends. Mask ROMs are extremely reliable Very true, and the clue is in the name. Unlike UVEPROMS, Flash-ROMS (analogue storage, see above), Mask ROMS are not programmed as such, but the data is put there at time of manufacturer by including, or not including, metal/silicon bits of the chip design ...
by mikeb
Sun Jun 16, 2019 7:38 pm
Forum: Technical questions
Topic: Telestrat failure?
Replies: 22
Views: 1820

Re: Telestrat failure?

Also UV-EPROMS (the ones with windows on) have varying voltage requirements. Not all programmers meet the spec and so the chip may not be fully programmed, which can lead to early failure. The data stored isn't digital/binary after all, but a level of analogue charge. It's only rendered binary by a ...
by mikeb
Wed Jun 05, 2019 5:11 pm
Forum: Hardware hacks and extensions
Topic: Composite video mod?
Replies: 12
Views: 884

Re: Composite video mod?

and a 'conversion table' with 4-bit accuracy (the PROM). The "conversion table" has small snippets of a sine-wave (very rough) in it, indexed by the two-bit counter from IC24, and also depending on the 3-bit value of colour (from 0 0 0=black to 1 1 1=white) produces the same 4.43MHz sine wave, but ...
by mikeb
Sat Jun 01, 2019 8:36 pm
Forum: Hardware hacks and extensions
Topic: Atmos with a Slice of Raspberry Pi
Replies: 9
Views: 827

Re: Atmos with a Slice of Raspberry Pi

I was thinking the use of the DPDT switch along with using diodes on the 14 way y cable I'll have to make would help isolate the Oric from the Teensy. I don't have a working rig yet so what I'm not sure about is if I mechanically isolate the 5v and 0v lines would the 4051 signal pins still have a c...
by mikeb
Tue May 28, 2019 4:59 pm
Forum: Hardware hacks and extensions
Topic: Atmos with a Slice of Raspberry Pi
Replies: 9
Views: 827

Re: Atmos with a Slice of Raspberry Pi

... wire a DPDT switch to a decent 2A 5V PSU and bypass/remove the regulator altogether and simply wire the switched 0v/5v lines to both the Pi and Oric - any thoughts on if this presents any concerns? That's a better approach, IMO, once you are on the "inside" of the regulator, supplying ground an...
by mikeb
Mon May 27, 2019 5:22 pm
Forum: Technical questions
Topic: 65c22
Replies: 15
Views: 1144

Re: 65c22

I see, thanks for the link/context The above diode suggestion by @iss will solve the problem (make sure it's in line with only the 65C22 leg, as per my caution on physical layout issues) -- the 65C22 having "totem pole" output means it will try and drive the line both HIGH (when idle) and LOW (when ...