Overclocking CPC @6/8 Mhz

[radu14m]

looks that i need o wait for my X-MEM to test this 
did you try to overclock the cpc to 8Mhz ? i struggle to find a 32Mhz crystal....

[TFM]

Yes, I tried, but in this case the Gate Array is definitely not quick enough. I think that most CPC's can make it with 6 MHz though.

I don't know if the X-MEM is quick enough to run with 6 MHz. But let me know it you do some tests.


Slowly I think again to get my 6128 up to 6 MHz (switchable back to 4 MHz of course) and make some stuff for it, because the screen resolution is far better. Also if the HxC would work - this would be awesome. If it doesn't work with 6 MHz, then a Firmware-Update could help IMHO.

[radu14m]

well, i swap also the z80 with a z80b, but it was not necesary. The original Z80 from zilog run also  @6Mhz without a problem. ( and did not get hot )
Memories are with 15ns not a problem for the new speed.

Some pictures:



The ideea with the switch is good, i use now a crystal socket and took him ouside the case - in that way i can swap the crystals easy. Now we need also a ROM for 6Mhz    
Looks like this :




some z80 used for tests





About the X-Mem maybe TotO can tell us more.....i modded my schneider cpc in order to test the Hxc and the X-mem @ 6 Mhz

Setting the CRTC every time is boring....

Who can fix the Hxc Firmware ? Jeff ?

[Bryce]

The FDC gets a direct signal from the main clock, you need to isolate this signal (at IC205 pin 13) and add a seperate 4Mhz clock crystal. The FDC clock doesn't need to be synced to the main clock, so it will work fine and you can then read standard disks. This could also be switched so you have "compatiblity" or "high density" modes.

Bryce.

[Ast]

CAN You explain me why do you want to overclock our cpc ? What Will really be the gain ?

[Neil79]

Would this overclock improve things with laggy areas of games? Like the R-Type homebrew on second level, Rick Dangerous 2 with laser beams etc going off. Shame we cant get an extension instead of changing crystals. Like an ACA accelerator 

[TotO]

I don't know if the X-MEM is quick enough to run with 6 MHz.

[TFM]

TotO's answer probably tells: YES! It is!


However, the question is valid. I know for example that the RRB has problems at 6 MHz, while my EPROM board has not. So, yes, IMHO it's needed to check expansion hardware.

[Bryce]

The MegaFlash would probably have problems, but it's not a hardware problem, it's a software issue. Delays required in the writing routines would be too short for the Flash. You'd need to write a 6/8Mhz version to correct the delays.

Bryce.

[TFM]

Instead of a fixed waiting time one can check bit 7 to wait for end of cycle.

[TotO]

If the flash code wait the IC chip to be ready instead of making a wait loop, it should be not a problem.
About the X-MEM, I have not made tests but the RAM is 55ns (90ns for ROM) and the CPC RAM is 120/150ns.

[radu14m]

Great TotO!

@TFM: it is possible to prepare a ROM that will automaticaly check the bit 7 ( end cycle check)and adjust the CRTC accordly for 4 or 6 mhz?

[Bryce]

If the flash code wait the IC chip to be ready instead of making a wait loop, it should be not a problem.
About the X-MEM, I have not made tests but the RAM is 55ns (90ns for ROM) and the CPC RAM is 120/150ns.

On the MegaFlash this isn't possible, because you would have to keep switching the read/write switch to check the ready signal.

Bryce.

[arnoldemu]

@radu14m: I don't see your pictures. Please post them again.

[radu14m]

The FDC gets a direct signal from the main clock, you need to isolate this signal (at IC205 pin 13) and add a seperate 4Mhz clock crystal. The FDC clock doesn't need to be synced to the main clock, so it will work fine and you can then read standard disks. This could also be switched so you have "compatiblity" or "high density" modes.

Bryce.

i like that ideea. Do you have a schematics for this ?
Also would be nice to have an integrate frecvency switch possibilty, without need to restart the system.
like a turbo button 

yestrday the pictures were fire..damn.

[Bryce]

No, but I could do some when I have time. Switching frequencies "on the fly" would be rather difficult as you would need to add circuitry so that only one crystal is being used and then being divided for the lower frequency. Not impossible, but complicated.

Bryce.

[arnoldemu]

@radu14m: I don't see your pictures. Please post them again.

I see them now.

I see lots of Z80's including soviet ones. 

And I see a 68000, planning to swap the z80 for a 68000?? 

[radu14m]

No, these are from my CPU collection

[TFM]

Great TotO!

@TFM: it is possible to prepare a ROM that will automatically check the bit 7 ( end cycle check)and adjust the CRTC accordingly for 4 or 6 MHz?

That should be doable with the X-MEM and the FlashGordon. 

[radu14m]

No, but I could do some when I have time. Switching frequencies "on the fly" would be rather difficult as you would need to add circuitry so that only one crystal is being used and then being divided for the lower frequency. Not impossible, but complicated.

Bryce.

Thats great Bryce !
Someyhing like ACA solution should be done for cpc too.

Pity that i cant use my HxC @6mhz

[Bryce]

Unfortunately, the CPCs architecture wasn't made for extrernal accelerators and second processors like the Amiga was.

Bryce.

[Munchausen]

That should be doable with the X-MEM and the FlashGordon. 

And symbiface, presumably? This would be very cool

[Bryce]

Ok, just messing about here with a concept for a possible "Accelerator" for the CPC. The idea is this. A single 24Mhz Clock with a divide by three circuit to bring it back down to 16Mhz. Solid-state switching to allow you to switch frequencies without resetting and a seperate 4Mhz clock for the FDC (this could also be made switchable if required). The PCB would be installed by removing IC117 and plugging this board into the (newly added) socket. It would also have a single wire that would need to be connected to IC205 Pin 13 (after disconnecting the pin from the mainboard). It looks complicated in the schematic, but actually it's only 4 ICs including the 74HC04 that was on the mainboard.

It's just a first draft/scribble and probably full of mistakes and potential for simplification, but I thought I'd upload it anyway, because (A) radu14m asked for one and (B) To get the discussion rolling.

All electronics members (and non-electronics members), feel free to criticise and pick holes in the design / schematic / concept

Bryce.

[radu14m]

It's amazing Bryce !!!!
thanks !

[Munchausen]

A single 24Mhz Clock with a divide by three circuit to bring it back down to 16Mhz.

Did you mean this? Because 24/3 = 8. You mean 2/3 (divide by 1.5) right?