For example, the 8250/16550 chip used to handle serial communication is still simulated by modern chipsets and is enumerated by ACPI as PNP0500/PNP0501. You can find datasheets for these chips.
However, any information on how the chip is wired to other devices on the motherboard (e.g. to the PIC) seems to be only present on various hobbyist websites, I can't find anything official.
Where do I find such documentation?
Edit: I want to clarify my question. I understand that discrete chips aren't used for simple functions anymore. However, for compatibility, the hardware must still look the same from the software perspective. If I stay with the 8250 example, the chip has modem signal outputs, like DTR and RTS, but it also has two general-purpose outputs, OUT1 and OUT2. On ATs, OUT2 controlled a gate that enabled/disabled the connection between the INTR output of 8250 and the IRQ4 input of the PIC. As such, OUT2 served as master enable for the UART interrupts.
This is what I meant by wiring. Although there is no external wiring for modern chipsets, if the chipset emulates the old UART and enumerates it as PNP0500, the software must still set the (nowadays virtual) OUT2 output to enable interrupts.
Now I'd like to know where the authoritative documentation for this behavior is. Surely, an OS writer doesn't have to read the specs of all (even future) chipsets to get the driver for PNP0500 right, does he?