I'm trying to interface with the Sega Saturn's 32KB Backup SRAM chip, and I was curious if anyone knew the speed the Saturn did this at. The datasheets for the various drop in replacements Sega used from model to model suggest they are capable of operating as fast as 70nS, which would clock it at around 14.28MHz, and I think I've read that the Saturn has an overall system bus speed of 14.3MHz. Although it would be extremely coincidental if the bus speed just happened to be the maximum a single RAM chip on the bus. Any suggestions? I know that several lines run directly to one of the SH2s.
Most of the machine operates at a 14.318Mhz master clock (4x the ntsc clock), or multiples of thereof (eg double that for the SH2s, half that for the VDP1 pixel clock, etc). Not sure about the bus speeds. SH1 and Sound have another clock nearby so it can be assumed they run at their own speeds - they are independent anyway. These apply to 352px mode. The machine can work at 320px resolution, in which case the master clock gets a 1708/1820 divider applied, dropping the system speeds. The machine boots up at 320px resolution. For PAL machines, you have a master clock of 17,734475 Mhz (4x PAL colour clock) fed through a 910/1135 divider according to datasheets. The VDP1 manual lists all the clocks under chapter 8. But if you just want to read the contents of the backup memory, there are many easier ways for that...
Does the RTC store it's time in the backup SRAM? If so, is it constantly being incremented? Or is the backup RAM strictly for game saves?
The backup ram is only for savegames. The RTC is inside the SMPC, and you can actually get the machine to lose the date but keep the saved games (happened to me often while tinkering).
