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Old 24 September 2015, 10:55   #326
Join Date: Jun 2010
Location: out in the wild
Posts: 1,135
Originally Posted by Akira View Post
That looks indeed very good, I don't know if I get the same performance out of my ACA620. Are there any benchmarks comparing the ACA620 to the ACA 122A?
Can the A620 be overclocked to 28Mhz?
Benchmarking an ECS accelerator against an AGA accelerator is not very informative, as chipram performance is twice as high on the A1200.

The ACA620 has been deveoped to be a 25MHz card. Memory clock is always at 50MHz, and this base clock is divided by 3 for the CPU, so it runs at exactly the top speed that it's specified for: 16.67 MHz.

Overclocking is possible, but you do it at your own risk. First of all, you should install a cooler on the CPU. With the cooler connecting the two mounting holes, the "do not close!" jumper is activated. If you close that jumper now, the CPU clock divider is changed to 2, so it runs at 25MHz.
Once again, you do this at your own risk. The SMD version of the 68EC020 can't dissipate heat very well, and a cooler is mandatory in that case. Since you are soldering on the card, you lose warranty.

Although the overclocked ACA620 is "only" 3MHz slower than the overclocked ACA1221, the latter will still be a good bit faster for two reasons: First of all, AGA systems allow faster chipram access, and second, the memory clock of the ACA1221 is much higher at over 85 MHz. With this higher frequency, I can do "cleanup cycles" (closing a row after an access) without any CPU wait states, and I can hide refresh cycles between two CPU accesses. This makes it slightly faster than the ACA1220 at the same clock speed, and considerably faster than the ACA620.

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