The AMSSIO interface is a RS232 interface by the dane, Martin Zacho. As opposed to other serial interfaces the AMSSIO is meant to be installed on top of the Z80 CPU in the CPC. However the circuit can easily be built on a breadboard and connected to the expansion port as well.
AMSSIO exists in 3 different versions.
A new and improved version is the AMSSIO II.
Technical
Connects between Z80 CPU and mainboard. Uses a 1.8432MHz oscillator, MC14411P bit rate generator, a 6850 ACIA, a MAX232 voltage converter, and 74LS04 and 74LS08 logic chips.
Port addresses, schematics, and differences between versions I-III are unknown (the AMSSIO webpage doesn't exist anymore).
Software
The software for AMSSIO can simulate a disk drive and a printer on a PC connected via RS-232. The software comes in two parts. The first part is for the CPC. It replaces relevant parts of the jump block, redirecting disc and printer access via RS-232. The second part is called CPCSHELL and runs on a PC under DOS or Linux. Part of the PC harddisk can be used as a giant CPC disk via this mechanism.
A spare PC can therefore be used as a method to add a cheap harddisk to the CPC. Although the software required on the CPC reduces compatibility somewhat it works for most well behaved applications and games that consist of a single binary (no special loader).
Schematics
AMSSIO version 1.0
PLEASE NOTE: The schematics and files has an error on pin 7 of the MC6850 (IRQ). It has been connected to Vcc, but should be left unconnected.