rkauer said:BTW: you cannot overclock a 25MHz unit to 40MHz! You'll end with a very broken CPU. 25MHz can be overclocked to 28MHz, tops. 33MHz units can go to 36~38MHz and 40MHz units can go up to 44~48MHz.
Overclocking the Commodore A3640 said:I have overclocked three of these boards, by replacing the 50MHz oscillator by one rated at 60MHz. This gives 30MHz for the 68040. All systems work reliably at this speed, and it's an ideal way to get some extra performance out of this board. I have heard of other people getting more. One user has been able to clock this board as high as 40MHz, and another I have heard of, has managed to get 37MHz. These two users were not able to get a lower speed of 33MHz, possibly because of the design of the A3640, which uses delay lines for part of it's clock circuitry. These delay lines provide a fixed amount of delay which becomes inappropriate when the clock frequency is changed too much. I suspect a "wrap around" effect occurs when the frequency is increased still further, the amount of delay once again becoming more or less correct over 37MHz or so. Recently I have become aware that it is possible to change the amount of delay from this delay line, so that it is now possible to overclock to frequencies such as 33MHz, and possibly more.
rkauer said:If you find a MC68040 (not the fry-an-egg XC68040), you can overclock even the 25MHz over 40MHz without issues (on 3.1 and 3.2 boards).
U401, U208, U207, U213, U203 and U400 have stickers. They all say "*-01" and stuff like "exlat", "term" "mapper", "rst", "lebus" and "oebus".rkauer said:Your board don't have any sticker?
rkauer said:Also there is the version printed on the board, near the socket.
get yourself an MC68040 full core @ 40mhz m8, much cooler!!! (XC's are toasty chippies)
once you have all your kit PM me, I am sure I can help. I have a 33mhz 040 version of the A3640 that I will do this mod too as well me thinks
Kin Hell said:I guess plugging in a 40Mhz CPU & a 80Mhz X-Tal is the only thing to do for being sure!