foone

instead they added a new CPU opcode called XCE: eXchange Carry with Emulation. It just takes the 9-bit status register and swaps the top bit (Emulation) and the bottom bit (Carry).

so since you can't just directly set the status register and affect the 9th bit, you instead set or unset the carry bit and then swap them around to change if the CPU is in 8bit or 16bit mode.

it's such a weird design. Should we expand the status register? add another one? implement some other way to trigger this? NAH FUCK IT, JUST WRITE AN INSTRUCTION TO SWAP AROUND THE CPU'S STATUS REGISTER

fun fact: every SNES game has to have this code at the beginning. Because the SNES boots up in 8-bit mode (as it uses a variant of the WDC 65C816), but all SNES games are 16-bit.

The SNES using the 65C816 also means that Apple was indirectly involved in the design of the SNES: Western Design Center (who designed it) after consulting with Apple on what they wanted for the next series of Apple II computers.

This is why the 65C816 has the 8-bit mode that's compatible with the 6502 (as Apple wanted Apple II compatiblity) but with more RAM. That's why it's natively 16bit, but with a 24bit address bus so it can use up to 16 megabytes of RAM.

But it can drop down into 8bit mode so it can run Apple II software.

And the "start in emulation mode" function means you don't have to have a firmware to put it in the right mode before the CPU turns on. That's pretty important for the SNES, since all the code that runs on the SNES CPU is on the cartridge.

tangent: So the Apple IIGS is named that because it stands for "Graphics and Sound", as it's got much better graphics and sound over the standard apple II line. The sound is provided by an Ensoniq 5503 DOC wavetable synth

Ensoniq was founded in 1983 as Peripheral Visions, by former MOS Tech engineers who had worked on the C64. Their plan was to build their own computer, and to raise funds for this project, they were working on making a computer keyboard for the Atari 2600.

However, something else happened in 1983: The video game market crashed (primarily in the US). So Atari canceled the keyboard project.

On top of that, Commodore sued, claiming they owned the keyboard project So they renamed themselves and pivoted into making synths.

Later, in 1998, Ensoniq was acquired by Creative, creators of the Sound Blaster.

So it's a company that started from Commodore and ended up as Creative. Weird. In any case, it's not the only legal trouble related to them... Apple also got sued because of their chip being in the Apple IIgs.

But it wasn't Commodore that sued Apple, this time. It was Apple.

See, there's two companies called Apple, and they've sued each other a few times. They are finally no longer having trouble, but that's rumored to be because one gave half a BILLION dollars to the other.

Around when that contract was running out, Epstein died. The Beatles had been considering how to move foward, and their solution was to found several companies of their own, including Apple Records.

So, Apple Records wasn't just The Beatles, as they signed a other acts the Beatles discovered or supported. But in any case, after 1969 the various Apple Corps companies were mostly merged, and they were informally known as just "Apple".

importantly one of the divisions that didn't exist after 1969 was Apple Electronics, which meant Apple Corps was mostly associated with music (and occasionally film).

And therefore it wasn't really a problem for three guys in Los Altos California to name their company Apple Computer, Inc, in 1977. Clearly they're distinct areas, so having the same name isn't a problem, right?

Well, no, in 1978 Apple Corps sued Apple Computer, for trademark infringement. That lawsuit continued until 1981, when Apple Computer paid Apple Corps 80,000$ to just drop it, and they laid out some conditions:

1. Apple Computer wouldn't enter the music business 2. Apple Corps wouldn't enter the computer business.

So now they're both happy, they both agree to stay out of each other's fields, and life can continue. Until 1986.

When Apple Computer releases their new computer, the Apple IIGS ("Graphics and Sound"), complete with the Ensoniq 5503 DOC chip right out of a professional synth keyboard!