Overclocking 68020?

[Marchie]

Anyone out there overclocked an 020? (I've heard they OC rather well.)

More to the point: I have an accelerator card in an A2000 running at 14Mhz (double the system clock). Is it simple (or even possible) to up that multiplier to 3/4 (ie: to 21/28Mhz)?

(Probably not, but just wondering...)

[Sandro]

the 020 accels at 14mhz and 28 mhz uses the 28 mhz crystal on the motherboard for the clock so it can't be overclocked

[jack-3d]

CPU 020 itself has no problem with slight overclock (for example Furia has 33 MHz EC020 clocked to 37 stable). In this case you can try exchange 28 MHz oscillator by 30 or 33 MHz, but I dont guarantee the other components (RAM, SCSI, ...) will like it. Question are your expectations? (I mean you may not even notice the speed increase at all) I would rather invest for 030 or 040 accelerator instead.

[Zetr0]

@Marchie

The quickest way of doubling the speed of the system is to add FAST RAM via the trapdoor port - however you can actually boost the the chip-set as it can be "clocked up" giving about a 20% performance boost.

You can achieve this simply by putting the machine into an NTSC mode.

However adding S/RAM via the PCMCIA port will actually slow the A1200 down by 10% as it has to shift from 32bit data / instructions to 16bit data / instructions.

I hope that helps.

[TroyWilkins]

Which card is the 020 on, that may help us determine how it could be overclocked, if it in fact can be?

@Zter0: I think you missed where they wrote that it's in an A2000 my friend.

[roondar]

Appologies for going off topic here.

Originally Posted by Zetr0

however you can actually boost the the chip-set as it can be "clocked up" giving about a 20% performance boost....

You can achieve this simply by putting the machine into an NTSC mode.

As far as I know and assuming the relevant part of the HRM* is correct for AGA as well (and it should be in this case), this is not true. You can run the Amiga in NTSC mode, and this will increase the refresh rate of the screen from 50 to 60Hz, but the chipset itself will not increase speed - not nearly by the needed ~17% at any rate.

Which means you can move graphics at a smoother rate, but you can move less pixels per frame (=fewer/smaller BOBs) than using PAL modes.

*) From the HRM: "The system clock speed for NTSC Amigas is 7.16 megahertz (PAL Amigas 7.09 megahertz). The clock for the blitter is the system clock."

Note that 7.16 vs 7.09 is only a ~1% difference, not the ~17% needed to keep pushing the same amount of pixels per frame.

[Kin Hell]

@ marchie

http://members.iinet.net.au/~davem2/...ock/a2620.html

[Marchie]

Thanks all, I'm learning more each day.

It's a Neuroth 68020 in case anyone's interested.

Originally Posted by jack-3d

Question are your expectations? (I mean you may not even notice the speed increase at all) I would rather invest for 030 or 040 accelerator instead.

Mostly to have fun seeing what my A2000 can do

Thanks for the link Kin Hell, I had seen that page (it's a top site all-round!). I understand that the A2620 (and my card too) seem to use the system clock for the CPU (the 68882 has it's own crystal which I have already overclocked from 40Mhz to 50Mhz). But just like PC's it must be using a multiplier (or if the system has a 28Mhz crystal as you all say, a divider?) to get 14Mhz, so, at least in theory, changing that circuit will change the multiplier/divider value to set a different clock speed (and potentially screw up the 32-bit memory and kill the whole card of course ). Guess I can't help but wonder if it's possible...

Anyways, thanks again, this is a fun discussion!

[pandy71]

Originally Posted by Marchie

Anyone out there overclocked an 020? (I've heard they OC rather well.)

More to the point: I have an accelerator card in an A2000 running at 14Mhz (double the system clock). Is it simple (or even possible) to up that multiplier to 3/4 (ie: to 21/28Mhz)?

(Probably not, but just wondering...)

Depend on semiconductor process - old (original 12.5 - 16.67MHz 68020 generation PGA encapsulated) was fabricated in different semiconductor process - new one even marked as slow probably will go even up to 50 - 60MHz depends on die (same is for modern CPU's, smaller characteristic diameter faster clocking possible).
You may consider to slightly increase power voltage (5.25 - 5.40V) to increase OC capabilities and you need to cool CPU well - nowadays GPU heat sinks are small and capable to dissipate more than 50W - they should be fine, rest of the circuit also should be cooled - it is advised to provide some airflow (proper shaping airflow should be sufficient - usually no need for more fan's than 1)