C&T F8680 emulation

[Torinde]

Interesting 186 variant with 26-bit addressing (64MB RAM): datasheets.

• uses bank switching for the space above 1MB?
• "maximum local system memory that is directly managed is 4MB" (page 20)... have to read more to understand what that refers to
• can it use ISA card(s) for expanded memory in addition, for a total of 64+32=96MB RAM?

Has a System Management feature "SuperState R".

Kind of related is VAutomation Turbo86/186 that has 24 bit addressing mode allowing for up to a 16Mbyte address space.

Related:

• C&T F8680 emulation - 186 with 26-bit addressing joncampbell123/dosbox-x#5261, C&T F8680 emulation 86Box/86Box#4922

[dbalsom]

Neat, but not going to happen unless someone wants to contribute it.

[Torinde]

I understand.

What is your opinion on how they implemented that 26-bit/64MB support?

• other 86/186 CPUs which support 24-bit/16MB seem to use custom addressing modes (e.g. NEC V33)
• EMS maximum seems to be 32MB, but if you compare F8680 (rev1.1) vs F8680A (rev2.0) datasheets you'll see they omitted the text mentioning a 32MB restriction...
• at the same time both F8680 datasheets mention a 4MB "local directly managed" memory.

[dbalsom]

no idea. unfortunately, with limited time, i can't investigate every little rabbit hole in early PC history.