Overclocking A3640

[Zac67]

What's the speed of your RAMs? 30 MHz requires <67 ns which can become difficult with the ZIPs in a 3k.

(25 MHz means a cycle time of 40 ns, the manuals states 80 ns or faster is required equalling two CPU cycles per RAM cycle. 30 MHz reduces the CPU cycle to 33 ns.)

[Zac67]

Using static column ZIPs (xxxx02) with an '030 is a bit faster for enabling its burst mode. The '040 burst mode is not supported by Ramsey anyway, so you can use fast page ZIPs or SIMMs as well (SIMMs are always FP).

With very fast SIMMs (<60 ns) you could try setting Ramsey to 16 MHz (J851 to 1-2), removing a memory wait state. This would really speed up things, esp. with an '040 - but I've never tried it. Anyone?

[Zac67]

(the A3000/4000 custom chips were actually designed to run @ 28 MHz and under-clocked to 25 MHz for production reasons

Erm.... no. The custom chips always need to run on 28 MHz or you wouldn't get anywhere near NTSC/PAL frequencies. The Amiga has two distinct busses that may be run asynchronously.

[Zac67]

Yeah, sorry - I applied "custom chips" to Agnus etc automatically. Of course the CPU side custom chips run 25 MHz. There are a some accelerator boards that overclock the mainboard slightly to 28 MHz.