AMSSIO
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.
Contents
Description
AMSSIO is a RS-232 serial interface for the CPC464 (and 664/6128) and it exists in three different versions which all uses the MC6850 asyncronous communication interface adapter (ACIA) from Motorola.
- The first version was based on components from the scrap yard. But the MC14411 is a bit bulky and by now rather old and somewhat hard to find. The second and third version was an attempt to work around the MC14411.
- Version 2 uses a 4060 ripple counter as clock generator. But it can be tricky to make it operate at 2.5 MHz. This was the reason for version 3...
- The version 3 uses a 74LS393 to divide the 4 MHz CPU clock by 26 to obtain the 153 kHz for the serial clock (9600 * 16).
"I couldn't get the software to receive faster than 9600 :-( But it was at least 4 times faster than the tape transfer rate :-)." All three versions are supposed to use the CPU socket in the CPC. The CPU socket on AMSSIO is meant to be a wire wrap socket. The CPU is removed from the CPC main board. AMSSIO is mounted in the empty socket and the CPU is placed in the 40 pin socket on the AMSSIO.
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
AMSSIO version 1.0 (6850-based, sixteen jumper-selectable clock sources)
AMSSIO version 2.0 (6850-based, four jumper-selectable clock sources)
AMSSIO version 3.0 (6850-based, single clock source)
- PLEASE NOTE: The schematics and files have a few errors:
- MC6850 pin 7 (/IRQ output, in v1-v3) is connected to Vcc, but should be left unconnected.
- The signal marked 153.8MHz (in v3) is, of course, 153.8kHz (4MHz/13/2).
- The photo seems to show v1 and uses 1.8432MHz crystal, whilst schematic v1 uses 10MHz (?)
- Note: The Z80 CPU shown in schematic is your CPC's built-in CPU (mounted piggy-back on the AMSSIO cart)
AMSSIO-II
AMSSIO-II (or AMSSIO version 4.0) (not 6850-based)
