@gloriouscow Interesting that S3 and S4 are one here (the 8087 datasheet says this too) which means if a system designer wanted to make separate address spaces for each segment register they wouldn't be able to use an 8087.

@gloriouscow So when access is made to the PCB it does go out to the bus. Wonder if I'll have to emulate that for some machine someday.

@gloriouscow Oh I lied, I have run into one. I have a us robotics 33.6 modem with a 80186eb. I've dumped the rom but haven't tried to emulate it yet. It also has a DSP 56k.

@gloriouscow I haven't run into any machines with those variants. They might have mostly been used in small embedded applications. If you check the manual for the EC version, it's even more different such as having an 8259 for the int controller.

@gloriouscow Yep (well I expanded on already written code for the ironman stewart off-road sound hardware). Irmx mode is only used by one machine, the ta alphatronic p60 which an xt compatible, maybe the only one with an 80186.

@gloriouscow Nope (although you can set it to cascade to a real 8259). Be aware that it isn't an 8259 and has very different programming registers.

@gloriouscow it acts like a normal int controller input it's not that it's weird but it requires the usual software control to setup the controller behavior, unmask and eio.

@gloriouscow Must have been removed in later variants. Too bad. Edit: or renamed to slave-master

@gloriouscow Note that the external int lines behave quite differently from the 8086 int inta lines. If you want to make it to work like the 8086 you can enable irmx mode in the relocation reg.

@gloriouscow Huh? No it's at 0xff00 at reset.

@gloriouscow The 80186 chip select unit allows setting 0-3 wait states for each chip select output. Maybe they just give a chance to change the wait state setting for the rom region just after reset.

@gloriouscow Also, I haven't checked myself but the datasheet says that the S3 and S4 status bits are always low at T2-4 rather than encoding the segment register so you might be able to look for that.

@gloriouscow Yes, I was about to suggest that. I was also thinking about writing to 0xff00, the default peripheral io address but then you'd have to look for the lack of output (and I'm not sure about that).

@gloriouscow FYI, I don't know if you need the INTA line but the 80186 doesn't have it unless you set IRMX mode in the relocation register.

@gloriouscow I added that to mame some years back. No one knows or cares but me.

@gloriouscow It's not quite the same but the pc-h98 has an 8bpp over 8 planes mode. NEC really did not want to make the upd7220 useless. Not much supported it and was overshadowed by the pc-9821 which has an 8bpp packed pixel mode.

@TerrorBite @gloriouscow
We have discussed floppy copy protection on discord.

@adrianyyy Trick question. The 80286 isn't an SOC.

@aaronsgiles https://www.betaarchive.com/wiki/index.php?title=Microsoft_KB_Archive/123443

@MrLovenstein Nanni: This is the worst copper ever.
~4000 years later: https://en.wikipedia.org/wiki/Complaint_tablet_to_Ea-nasir