Amiga questions you've always been too embarrassed to ask

[Jope]

Usually a male to female RS232 cable has all the pins connected straight through, so yes. Make sure you avoid null modem cables, sometimes they are available with M<->F connectors too.

[Predseda]

Question:

What I read in amiga hardware database about A1200 motherboard:

A 68881 or 68882 floating point unit can be installed on the motherboard, but no socket is provided.

I pressume it is referring to the blank white square on the mobo between Alice and CPU. Does that mean if I would solder 68881 or 68882 FPU to that place, it would work?

[Amiga1992]

Originally Posted by Predseda

I pressume it is referring to the blank white square on the mobo between Alice and CPU. Does that mean if I would solder 68881 or 68882 FPU to that place, it would work?

I'm not sure, because you would need a slot also for the crystal, unless it is there and I don't see it.
If you don't have that I think the FPU would run at the same speed as the CPU and that's kind of silly.

In any case an FPU is so pointless, it's hardly worth the huge effort.

[Amiga4000]

It can be done, referred to this link...

https://www.facebook.com/media/set/?...6499869&type=3

But, the mod conflicts with all ACA boards.

Per this EAB discussion...

http://eab.abime.net/showthread.php?t=69974

[Amiga1992]

Cool, good to see someone tried.
So, the speed of the FPU would be 14Mhz then.
This is not worth all that effort :P especially if it conflicts with other boards.

That brings me to a question for this thread: can you overclock the standard EC020 by changing the crystal?

[Jope]

No, you can't overclock it that easily.. The motherboard is synchronous.. All timings (custom chip, video output frequencies) will be off. The solution: install a turbo card into the trapdoor slot. :-)

[Amiga1992]

Makes sense! Thanks, just thought I'd ask, I knew it was a stupid question

[nogginthenog]

Originally Posted by Jope

No, you can't overclock it that easily.. The motherboard is synchronous.. All timings (custom chip, video output frequencies) will be off. The solution: install a turbo card into the trapdoor slot. :-)

Many years ago when I was a student I was living in the Netherlands. There was a local computer fair so I popped along.

Found a guy selling a 16Mhz 68000 (68010?) on a board so I bought it and popped it in my A500. It worked, but the Amiga clock (i.e. date/time) ran twice as fast! (or at least faster)

No idea what happened to that (or the A500).

[Predseda]

Originally Posted by nogginthenog

Many years ago when I was a student I was living in the Netherlands. There was a local computer fair so I popped along.

Found a guy selling a 16Mhz 68000 (68010?) on a board so I bought it and popped it in my A500. It worked, but the Amiga clock (i.e. date/time) ran twice as fast! (or at least faster)

No idea what happened to that (or the A500).

So you constructed a time machine!

[Anakirob]

Originally Posted by Jope

No, you can't overclock it that easily.. The motherboard is synchronous.. All timings (custom chip, video output frequencies) will be off. The solution: install a turbo card into the trapdoor slot. :-)

Would it be possible to simply double the clock speed?
I'm not asking if this would be sensible to do, or even if the 020 fitted in the A1200 could do it without bursting into flames just is it theoretically possible to overclock the CPU on the motherboard by a power of 2?

[zipper]

Yes - but nothing would work...

[plasmab]

Originally Posted by thomas

That said, the big question is: why does the drive not need to click when a disk is in the drive?

The disk drive change signal is only valid (i.e. you can only detect a disk change) after you step the disk on many (most?) of the drives that have appeared in Amigas over the years. Thats why they step so the the OS can see if the drive has changed.

EDIT: Goodness me i hadnt seen that there was 68 pages on this thread. Sorry if this has already been answered 20 times.

[Jope]

Originally Posted by plasmab

The disk drive change signal is only valid (i.e. you can only detect a disk change) after you step the disk on many (most?) of the drives that have appeared in Amigas over the years. Thats why they step so the the OS can see if the drive has changed.

I'm too lazy to double check, but I think this is actually in Shugart's original spec.. The DC flip flop is clocked by the step signal, thus all drive mechanisms exhibit this behaviour.

EDIT: Goodness me i hadnt seen that there was 68 pages on this thread. Sorry if this has already been answered 20 times.

Hehe.. It's been going on for a while now. :-)

[thomas]

Originally Posted by plasmab

The disk drive change signal is only valid (i.e. you can only detect a disk change) after you step the disk on many (most?) of the drives that have appeared in Amigas over the years. Thats why they step so the the OS can see if the drive has changed.

This does not answer my question. You say (like everybody else) that disk *change* is recognised after a head step.

But it only needs to step while there is no disk in the drive.

This means to recognise disk *insertion* the drive needs to step regularly.

But to recognise disk *removal* it does not need to click at all.

Now the question again: when the disk *change* signal is only valid after a step, why does it need to step only if the drive is empty but not when there is a disk in the drive.

[Daedalus]

Just speculating here, but is a head move not initiated internally by the drive when a disk is ejected in order to home the heads? This would validate the new output automatically, making it available to the Amiga to read without a step command.

[Toni Wilen]

Originally Posted by thomas

Now the question again: when the disk *change* signal is only valid after a step, why does it need to step only if the drive is empty but not when there is a disk in the drive.

Perhaps step requirement was originally free floppy inserted signal's de-bounce circuit? Also I don't think original drive/interface designer (shugart) expected some weird future computer to (ab)use it to detect inserted disks automatically. (Instead of traditional: computer asks for disk, user inserts disks, presses key -> computer does single step -> was there disk or not?).

Originally Posted by Daedalus

Just speculating here, but is a head move not initiated internally by the drive when a disk is ejected in order to home the heads?

Shugart-like disk drives don't do automatic seeks.

[TroyWilkins]

Originally Posted by Anakirob

Would it be possible to simply double the clock speed?
I'm not asking if this would be sensible to do, or even if the 020 fitted in the A1200 could do it without bursting into flames just is it theoretically possible to overclock the CPU on the motherboard by a power of 2?

I could be wrong here, but my understanding is that in the 68000 based models, as well as the A1200 and CD32, the system clock is set by one crystal, and then all the other clocks are exact divisions of those clocks.

My understanding is that on PAL machines, the crystal is 28.37516MHz and NTSC it will be 28.63636 MHz. On a 68000 machine, this is divided by 4 to get the CPU clock speed (7.09MHz for PAL, 7.15MHz for NTSC), and on the 1200 and CD32, it's divided by 2 to get the CPU clock speed (14.18 for PAL, 14.31MHz for NTSC). I could be wrong here with the exact numbers, particularly with the 1200 and CD32, but my understanding is this is how it's set, and the video and audio circuitry is also set with these clocks, using a divisor where necessary.

The problem isn't that the CPUs can't be clocked higher, it's that if the CPU was clocked higher (or lower), all the other clocks speeds would be messed up, because they wouldn't be exact divisions. To fix this would be far more hassle than it's worth. At least, that's my understanding from my layman's reading of the schematics for the Amiga models. This isn't the case in A3000 and A4000, nor in any model with an accelerator card, as then the CPU doesn't have to run synchronously with the system bus, and the CPU gets it's clock from a different source.

If I'm wrong here I'm sure someone will correct me.

[methodman]

Why won't Amiga Forever unzip zip files when WinUae can?

[Nibbler]

QUESTION :

Is it ok to just Assign ENV: ENVARC:

? Why HappyENV ? Is this problematic ?

[idrougge]

It is OK, but still a bad idea since the "use" option in prefs programs will no longer work.