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View topic - Sega 8-bit media interoperability check/confirmation

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  • Joined: 22 Aug 2011
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Sega 8-bit media interoperability check/confirmation
Post Posted: Mon Jan 24, 2022 8:11 pm
Recently, I've been toying with the idea of getting an FPGA and programming it to emulate the Z80 and associated support chips in order to create a breadboarded, all-in-one Sega 8-bit dev console. While researching the idea, I had a few unanswered questions regarding the interoperability of various software media.

I'll summarize what I know/can confirm (by console):

SG-1000
* Used cartidges
* Used MkI Sega Cards via the Card Catcher
* Used cassettes via the SR-1000 Data Recorder (via the the SK-1100 keyboard)

SC-3000
* Used cartidges (with built-in RAM)
* Used MkI Sega Cards via the Card Catcher
* Used cassettes via the SR-1000 Data Recorder
* Used 3" diskettes via the SF-7000 Super Control Station

Q1) A Sega Card game is written to utilize the 8kB RAM/16k VRAM of the SG-1000, but is used via Card Catcher on an SC-3000, which only has 2kB of onboard RAM. What happens? I doubt thrashing was common, but slowdown, perhaps?

Q2) Similar to the above, but with cassette data: I am totally unfamiliar with cassttes as a storage medium for software (only as mass storage), so any elightenment here would be helpful, especially for software written with the larger 34kB of RAM in mind.

Q3) I assume the SF-7000 diskettes could access the whole system's RAM, from the (16/32kB) BASIC cart to the SF-7000's additional 64kB, but could cartridges? Cassettes? Cards?
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Post Posted: Mon Jan 24, 2022 10:39 pm
SG-1000 has 1KB RAM, so there is presumably software that works on SC-3000 but not SG-1000 with keyboard+tape. I think all carts are compatible though. It would manifest as failure to work at all; thrashing is a feature of virtual memory and disk paging, that doesn’t exist on these computers.

On all these systems, it is possible to use cartridge memory to supplement and replace system RAM; but it would be complicated to use them all at once as they conflict in address space. So for example, I think the SF-7000 has 64KB RAM inside and simply disables the SC-3000 2KB RAM. To use it would be extra hassle as it would need to support multiple memory maps and manage the cases where the data it wants is not in memory.

For both tape and disks, the pattern is simply to load data/code to RAM and run it from there.
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