This interface was originally described in the book "[[Maschinenspracheprogramme und Hardware-Erweiterungen für Schneider CPC's]]" written by [[Paul Bauriedl]], released by IDEA Verlag in 1987. Around mid-nineties, Tim Riemann has circulated the schematic as GIF in the internet.
The circuit is nearly indentical to the [[Schneider RS232 Interface]]from 1985, both circuits are using a Z80 STI, both mapped to the same I/O port addresses. Both circuits seem to be driven by the 4MHz signal on the CPC's expansion port, so even the the timings should be 100% compatible. The only difference is that the DIY circuit uses more logic chips for decoding of the I/O port addresses (the extra chips are just more over-complicated, not actually better). Another difference, concerning the power supply, is that the Schneider circuit contains 2 diodes and 2 diodes for converting ~7V AC to +/-7V DC.
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Image:SchneiderSioManualPage2.jpg|Schneider's Schematic (1985)Image:NoPicture.png|Paul Bauriedl's's Schematic (1987)Image:Tim Riemann RS232.gif|Tim Riemann's Schematic(1996)
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