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/  Forum Index
   /  Classic Amiga Hardware
      /  Does an FPU need a crystal?
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DustyA1200 
Does an FPU need a crystal?
Posted on 16-Oct-2017 17:12:38
#1 ]
Member
Joined: 9-Oct-2017
Posts: 12
From: Middle of the UK

I have an M1207 8MB RAM card on my A1200, not currently being detected but its
not in the case at present so will look into that after putting it all back together.

The card has an FPU socket and a socket marked XTAL, but the XTAL socket doesnt appear
to have any connectors attached.

Does an FPU need a crystal to work?

Thanks

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amigakit 
Re: Does an FPU need a crystal?
Posted on 16-Oct-2017 17:40:16
#2 ]
Amiga Kit
Joined: 28-Jun-2004
Posts: 2515
From: www.amigakit.com

@DustyA1200

Hi

Yes it will need a crystal matching the speed of the FPU (and the speed that the card supports)

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PR 
Re: Does an FPU need a crystal?
Posted on 16-Oct-2017 20:44:36
#3 ]
Super Member
Joined: 1-Sep-2004
Posts: 1961
From: Suomi-Finland

A friend gave me a small box of different metal coloured in different Mhz, four legs to insert, maybe remeber wrong but it could be placed in a turbo card.

---

Found the safe, 20mhz and 66,6660 mhz left, these were for the card.
Maybe for the prosessor but Yes the FPU needs too.



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Daedalus 
Re: Does an FPU need a crystal?
Posted on 17-Oct-2017 11:30:03
#4 ]
Super Member
Joined: 14-Jul-2003
Posts: 1680
From: Glasgow - UK, Irish born

@DustyA1200

For a little bit more detail: FPUs do require a clock signal, however usually those RAM+FPU cards have a jumper setting that lets you choose to use the 14MHz motherboard clock or an optional crystal. From looking at photos of your board it seems that jumper is beside the empty crystal socket. So you probably don't strictly need a crystal, but with most FPUs being rated higher than 14MHz, it might be worthwhile hunting down a matching crystal.

As for the card not being detected, is the card itself showing up in the early startup screen? That should happen even if the RAM isn't present or is faulty. If the RAM isn't showing up in Workbench, are you sure the jumpers are set right? Are you sure the SIMM itself is working?

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DustyA1200 
Re: Does an FPU need a crystal?
Posted on 18-Oct-2017 22:27:17
#5 ]
Member
Joined: 9-Oct-2017
Posts: 12
From: Middle of the UK

Thanks Guys, I did try replying last night but as i was checking the pins on the ram board
Windows 10 decided to update and restart. Losing everything.

Yes there is a jumper saying INT / CPU. Currently on Internal where it has been all its life.

I assumed the XTAL socket to be a 10pin one with 4 additional corner posts soldered to
the board for stability. But a closer look last night shows that the 4 corners to be soldered
to traces on the underside of the board and what appear to be connectors on the top.
None of the centre set of 10 pins have anything attached to them.

Just tried the board and it booted fine with the 8mb showing, booted to the CF card with
no issues and my games worked. The other day it booted but games wouldnt run saying
not enough memory.

Are the crystals just 2 pin ones? Or something not right with my socket? Would a picture
help?

Thanks

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DustyA1200 
Re: Does an FPU need a crystal?
Posted on 18-Oct-2017 22:32:02
#6 ]
Member
Joined: 9-Oct-2017
Posts: 12
From: Middle of the UK

PS. Will a faster FPU fit and work but at the slower speed?

ie. Seen some very cheap 40mhz FPU's will these fit and work even at 14mhz?

Thanks

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Rob 
Re: Does an FPU need a crystal?
Posted on 18-Oct-2017 23:02:17
#7 ]
Elite Member
Joined: 20-Mar-2003
Posts: 6344
From: S.Wales

@DustyA1200

Quote:
Seen some very cheap 40mhz FPU's will these fit and work even at 14mhz?


It will work just like a 14Mhz part.

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Daedalus 
Re: Does an FPU need a crystal?
Posted on 18-Oct-2017 23:18:08
#8 ]
Super Member
Joined: 14-Jul-2003
Posts: 1680
From: Glasgow - UK, Irish born

@DustyA1200

Normally the crystals are 4 pin. There are two common sizes that are used on Amiga boards, a square and a longer rectangular one. They happen to fit the corner pins of an 8 or 14 pin DIL socket, so these are often used as a socket for crystals with the inner pins removed. Some boards even have both sets in one socket so either size can be fitted.

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DustyA1200 
Re: Does an FPU need a crystal?
Posted on 19-Oct-2017 0:23:47
#9 ]
Member
Joined: 9-Oct-2017
Posts: 12
From: Middle of the UK

@Rob
@Daedalus

Thanks Rob, So a sub £2 040 FPU (assuming it works) will be happy at 14mhz. Maybe
onto a bargain assuming it works. Or your going to tell me they are ony a £ normally.

Thanks Daedalus, So im not mad and not a rogue part then. Its a 14pin socket where
only 4 pins are used, made me happy now.

Just need 40mhz crystal :) Or will you now tell me these are obsolete or £1million?
Only ever seen 2 pin crystals.

Turning out to be a good day. Just been playing Body Blows, one of my all time favourites.

Thanks.

Even my daughter is interested and enjoyed beating me at my (ex) favourite game :)

Need to sort my games out, she dug out a box of floppies and typical that box was mostly
coverdisks.

Although I beat her a lot with Bomberman/Blitz Bomber? I remember the days of a few
beers and a few friends with a 4way adapter into the early hours.

Stuff arrived to whiten the cases and next task is sort the joysticks out. This one turns
left only, this one moves all directions but the fire buttons do not work, this ones a bit
iffy all around etc etc...

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PR 
Re: Does an FPU need a crystal?
Posted on 19-Oct-2017 6:26:07
#10 ]
Super Member
Joined: 1-Sep-2004
Posts: 1961
From: Suomi-Finland

Well said before from the jumpers- Used to change with tools squisers or how do You say it. Also changed an cpu for the A1. Many pins. Earthing first from static electricity.

040 or 060, FPU or not if recalling right in some turbocards, memory jumpers too.

My Girls ask also occasionally can we Daddy play or draw with the Amiga?

A Good time, everytime.


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Daedalus 
Re: Does an FPU need a crystal?
Posted on 19-Oct-2017 8:12:54
#11 ]
Super Member
Joined: 14-Jul-2003
Posts: 1680
From: Glasgow - UK, Irish born

@DustyA1200

I'm guessing you mean 40MHz FPU, and not 040 FPU (which is a different thing entirely...)? Yep, there are 2 pin varieties, which are actually the crystals. The 4-pin varieties are technically more than just the crystal, so are often referred to as oscillators or crystal oscillators.

Anyway, they aren't obsolete, though they are less used these days. Still, any big electronics supplier should be able to sort you out, and I'm sure they show up on eBay. Farnell have this one for example. A 33MHz one will do as well if you can't find a 40MHz one. Bear in mind however that an FPU makes no difference to the speed of the machine except for with particular software, such as 3D rendering or audio processing. Your games will all run at the same speed.

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DustyA1200 
Re: Does an FPU need a crystal?
Posted on 19-Oct-2017 10:21:09
#12 ]
Member
Joined: 9-Oct-2017
Posts: 12
From: Middle of the UK

@Daedalus

Yeah its the 68882 40Mhz FPU (Motorola). I spotted the same chip in a photo whilst
doing my homework on the M1207 board.

I searched ebay and one popped up very cheap. Thought at that price it was worth a gamble
and crossed my fingers that it would fit :)

It was only after that I thought the XTAL socket needed more pins.

I do not remember any games lagging so an accelerator card would probably be wasted on me. Only bought because it was super cheap. Ordered a couple of crystals off ebay about £3.60 for a 30 and 40mhz. Thinking of underclocking it to 30. But i was tempted to overclock but thinking what will actually use it? Paint or the megalosound box?

I am from an age where swapping 6 or 7 floppies to play a game was fast, comparing to the tape loading VIC20 that i had before it.

But with the tapes i could pause or skip a second or so of the tape and sometimes it would allow access to the source code.

Thanks for the help. What next :)

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DustyA1200 
Re: Does an FPU need a crystal?
Posted on 25-Oct-2017 3:07:11
#13 ]
Member
Joined: 9-Oct-2017
Posts: 12
From: Middle of the UK

FPU works a treat :)

Maybe my imagination but it appears to startup a little faster?

I think i may have found the issue of it not being detected, a jumper on the expansion board
was loose. The jumper is marked memory on.

Odd how a jumper could come loose when not used. Never had that happen before.

Only running the FPU at 30mhz at the moment, wondering if they get hot? Or is it so little
used that it stays cool?

But for £2.84 for the 68882 (40mhz) and £1.04x2 for the crystals (30 and 40mhz) it was
worth getting. What would the FPU have cost in the late 90's?

Bough a UV lamp to help whiten the cases and partially done the mouse so far, seems
to be working well. Its the VIC20 and the A500 which are the worst affected though.



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