14mhz Accelerator for A500 -Les Ayling -------------------------- Welcome once again to cheapskates corner, where we try and buy the world for a song. This time around we shall increase the speed of the processor to just over 14Mhz, double the standard speed, for under $25 !!!! You will need the following - 1. an MC68000p12A 16MHz processor. These are available in Sydney from VSI electronics, 16 DICKSON ave ARTARMON 2064 ph (02)4398622 cost is $18.90 plus tax ($22.68 tax inc.) 2. a 74F74 D type flip flop. Geoff wood at Lane Cove or Rod Irving should keep them. 3. a few short lengths of hook-up wire. 4. a SPDT switch. Refer to the accompanying circuit diagram Note: Keep the leads to the switch as SHORT as possible. The circuit is relatively straight forward. the 74F74 is wired as a positive edge triggered divide by two circuit, which provides the alternate clock frequency of 14.18Mhz approxiamately. The old 68000 8Mhz processor is removed and replaced with the 16Mhz version which has is clock pin (15) bent out horizontally so we can connect our new circuitry to it. The SPDT switch either connects the normal 7Mhz signal or the new 14Mhz signal to the 68000's clock input. The switch can be changed while the machine is on, however it will simply lock up. Just reset as usual from the keyboard once you have changed speed. (Check the mod further down for info for changing on the fly!) I have a revision 5 board with new 1.3 roms which cope with the new speed quite happily. Using the program CRAMDEN-SI from MEGADISC 10 to compare the difference the mod makes : The standard position gives- performance relative to amiga 1000 : 1.0 performance relative to ibm pc/xt : 3.2 On high speed the performance is- performance relative to amiga 1000 : 1.7 performance relative to ibm pc/xt : 5.2 so roughly a 70% increase in performance. Even though the clock speed is doubled to the processor, the performance dosen't increase to 2.0 because the agnus and the other support chips are still running at the same speed as before thus holding the processor up for a slightly higher percentage of the total time than before. This mod basically gives the same capability as the CMI accelerator board priced at $399 in Sydney, with the exception that it isn't software controlled. However when it's only costing 1/16th the price one cant really complain!!. The machine should work on the 1000 and 2000 however the pin numbers may be different. I suggest you compare the a500 schematics with that of your machine and make note of the differences. #addendum# One machine this mod was carried out on had trouble with the one of the disk drives at high speed. It appeared to be trying to step the head of the internal drive faster than the drive could physically move and refused to boot. When I connected a drive with a 5ms track-track access time and booted off of it the problem dissappeared. I have a patch for this problem for normal DOS disks to slow down the step rate which sits in the boot sector. It may be a problem however for protected software or non-standard boot sector type programs. Don't despair however the patch is very small and should fit in somewhere anyway. Just drop me a line. If your machine exhibits the problem, the patch disk is available DIRECT from me with various usefull disk speedup utils and a Trackdisk step-rate alteration program, plus loads of other priceless information on gurus, reset program flow, diagnostics all on an ARP1.3 system disk for the princely sum of $5 !! There should be no problem with HARD disks however if anyone encounters any please let me know........thanks. -*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* 14mhz Accelerator ----------------- The hack to accelerate your Amiga to 14MHz has been published in countless articles, but I may as well include a brief description of it here. The hack involves removing the original 68000 from your Amiga and substituting a version rated at 16MHz (confusingly called the 68000P-12; the Motorola chips have "16MHz" stamped on them, but the SGS-Thompson clones do not). The clock pin is bent out and soldered to the output of a divide-by-2 counter whose input is connected to the base 28MHz clock. THIS MODIFICATION SHOULD BE INSTALLED WITH A SWITCH !! If not, you WILL (not may) find that some games will refuse to load because they use timing-dependent loaders. Aside from the problem mentioned above, the only compatibility down-side to this modification is that some floppy drives will not handle the increased step rate. If you find that your drives give read/write errors at the high speed, you can either replace them or run a program called "DFDelay" to slow down the step rate. (If df0: will not work, you have a problem. Try swapping df1: for df0: - to do which you will need a Commodore df1:. The mechanisms used in the old A1010 drives are EXTREMELY reliable and much quieter than the new rubbishy things; if you have an A1010, you can be fairly certain that it will support the new speed). To perform the mod, remove your old 68000 and embed it in a perspex block for future reference. Now rig half of a 74S74 dual D bistable as a divide-by-2 counter. Connect the input of this to a convenient take-off point of the 28MHz clock line on the motherboard (I use pin #34 of Agnus, but anywhere will do). Now bend out pin 15 of the new CPU and solder a wire to this pin. Take a piece of stiff telephone wire, strip approx. 5mm of insulation from one end, and stick this end down pin 15 of the 68000 socket. Insert the new CPU in the socket and verify that pin 15 is well clear of the wire in the socket. Now wire a SPDT switch as follows : BACK VIEW +---+ When held as shown UP=7.14MHz, To output of divide-by-2 counter -+-o | DOWN=14.28MHz To pin 15 of 68000 -+-o | To wire in pin 15 of 68000 socket -+-o | +---+ The 74S74 should be mounted somewhere convenient; I break off all the unused pins, bend the remaining pins out, and stick the chip on top of one of the data path IC's; this has the advantage of allowing me to take power directly off the existing components rather than stringing yet another pair of wires through the machine. If you only have chip and/or slow memory then your machine will run at approximately 150% normal speed (on CPU-intensive operations; DMA rates will be unchanged). If you have true fast-RAM then code running from fast-RAM will execute at close to 200% of normal speed. Try placing a large perpective brush with anti-aliasing HIGH in DeluxePaint III (or IV !) and you will see the speed increase. -*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* ENHANCED ACCELERATOR by Ray Taylor This is an enhancement of the cheap accelerator project published in Megadisc 14. That project had a problem that caused the system to crash if you tried to change speed. The extra chips will act to delay the change of speed until the two clock signals are at the same logic level. This should overcome the problem of crashing. The circuit also overcomes the problem with the length of leads between the clock signals and the switch. I have not been able to test this because everyone else must have beaten me to VSI Electronics and bought all the 16Mhz 68000 processors. I'm waiting for new stocks. Keep up the good work with your useful magazine. I've learnt more from this magazine than I have from all the manuals, books and magazine articles I've read. -*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* HEAT PROBLEM ON 16MHZ 68000 - Ian Mills Quite a while after I upgraded to 14Mhz I was pottering around with Amy's internals and my hand brushed the 68000. It came as quite a shock to find it hot enough to fry an egg near the clock input pin. I quickly powered off suspecting I had dropped something in causing a short. Upon inspection, it seems this is normal, to run at 16Mhz the 68000 must use more power hence more heat dissipated. I rectified this by mounting a small heatsink directly on the 68000 near the clock input. It is held in place by a blob of heatsink compound. In the two months mine ran without the heatsink, I didn't experience any problems. Too much heat can cause computer chips to behave erratically, and ultimately, cause irreparable damage. Now the weather is warming up, it may raise the temperature high enough to cause problems. Due to the fan and forced air cooling in a 2000, the 68000 should be cooler than a 500, but the few cents spent on a heatsink is a good investment when you consider a 16Mhz 68000 costs about $24. -*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* FURTHER MODIFICATIONS to Les Ayling's 7 - 14 Mhz Upgrade. Changing Speeds 'On the Fly' without a re-boot. Ian Mills PO Box 429 Artarmon 2064 NSW Brief : It will allow you to change speeds without rebooting. It can also be used in a slightly different way, as described at the end. Disclaimer : The same as always ! Your warranty is already void if you did Les's original upgrade ! I take no responsibility for any modification you may do resulting from this article. Background : In his article, Les stated that the CPU must be reset after changing speeds, as the 68000 got upset when its speed was changed inelegantly. This got me thinking, as he also said the commercial version supported a change in speed 'on the fly'. It must be possible, but how ...... Most CPUs have a number of 'Non Maskable Interupts' (NMI) that are used for low level communications between other chips or CPUs, and our 68000 is no exception. It has a NMI called HALT that is connected to pin 17. Normally it is high, but by pulling it low, the 68000 will finish its current instruction and wait until HALT goes high again. The HALT signal on the Amiga 68000 is connected to GARY's pin 42. GARY pulls HALT low during the keyboard reset sequence (Ctrl, Amiga, Amiga). Halt also is connected to the expansion edge connector on the left hand side of the Amiga 500 (pin 55). Parts: 1 x SPST switch Hook-up wire Modification: Connect a wire from ground to one side of the switch. Connect the other side of the switch to pin 17 on the 68000 or 55 on the expansion bus. Mount the switch near the 14 - 7 Mhz switch. Now to change speeds, halt the CPU by throwing our new switch, select the other speed via the original switch, then allow the CPU to continue by turning off the halt switch. Variations to this Modification : The fact that pulling HALT low causes the CPU to stop and wait may be a usable feature for some users. It would be the ultimate "Control P" for gamers or for a close look at a fast animation. Another use could be a key-switch rather than a toggle switch to keep unwanted meddlers out of your system. -*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* ACCELERATOR NOTES by Leslie Ayling Here are a few problems which some people had which don't appear obvious at first. 1. If you are using ribbon cable to the switch, make sure to separate the conductors as some ribbon cables exhibit a cross-conductor capacitance. Hence the ground wires separating the various signals on the disk-drive connector for example. This could stop the system working at all. 2. Make SURE that you are supplied with the 16MHz version of the processor. The 12.5MHz version carries a similar part number but is not up to our demands. The 16MHz version should have "16MHz" printed on its case underneath the Motorola part number. 3. I have recently purchased an A590 hard drive and have found that the accelerator works fine with it, with or without 2 meg of ram installed. 4. Since there have been many enquiries from A1000 users, next issue I will probably describe the adjustments needed for that computer.