IIRC, the 68hc705 was one of those chips that included some "Rom monitor" functionality ST if you started it with the right cystal and strapping, you could speak async to a tiny bit of code. And that tiny bit of code could be used to load some code into RAM that could bootstrap the rest of the chip, or something like that.
Trying to find the details, it seems that they depended on exactly which chip you have.