After viewing a few cart board pics I noticed that the SA-1 has no oscillator, crystal or resonator. The documentation says the SA-1 can run up to 10.25Mhz but the only two clocks fed to the cart is SYSCK(P57) and MCK(P1). MCK appears to run at 5.369MHz based off the schematics (21.37727Mhz through two inverters) and I imagine that SYSCK is one of the 3.58 MHz, 2.68 MHz, or 1.79 MHz based off SNES processor settings. None of these speeds are exact multiples of each other so how do you sync the data over the cart connector?
My only guess is:
MCK is SA-1 core clock. Can be faster if games need it but apparently none did. The whole SA-1 and its peripherals run off this clock. When the SNES access RAM/ROM/IMEM that bus is being driven via SYSCK and the SA-1 has some magic inside that gives exclusive access and handles the clock errors. That seems a bit odd to me but the whole transparent bus the SA-1 employs is pretty unique.
If my guess is correct then I can communicate with the cart at any speed, a few khz up to MCK without any syncing required. Anybody know for sure?
My only guess is:
MCK is SA-1 core clock. Can be faster if games need it but apparently none did. The whole SA-1 and its peripherals run off this clock. When the SNES access RAM/ROM/IMEM that bus is being driven via SYSCK and the SA-1 has some magic inside that gives exclusive access and handles the clock errors. That seems a bit odd to me but the whole transparent bus the SA-1 employs is pretty unique.
If my guess is correct then I can communicate with the cart at any speed, a few khz up to MCK without any syncing required. Anybody know for sure?