== Intro ==
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 it was turned into a single package and 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 [[Media:Mostek_3801_Data.pdf|Z80 STI]], both mapped to the same I/O port addresses. Both circuits are driven by the 4MHz signal on the CPC's expansion port, and connect CTS/RTS/DSR/DTR to the same pins, so they are (almost) 100% compatible. Some differences:
* The Schneider circuit additionally implements CHRDET.
* The Schneider circuit contains 2 diodes and 2 diodes capacitors for converting ~8V AC to +8V/-8V DC.
* The Schneider circuit uses only 2 chips for port decoding (the overcomplicated DIY uses 5 chips for exactly the same purpose)
Image:SchneiderSioManualPage2.jpg|Schneider's Schematic (1985)
Image:NoPicture.png|Paul Bauriedl's Schematic (1987)
Image:Tim Riemann RS232.gif|Tim Riemann's Z80 STI Schematic (1996)
</gallery>
First about the connection plan: You need a power supply that supports +9V,-9V and 5V. Connect all pins. You have to connect D0..D7 from the adressbus with the Z80 STI. You have to connect D0 with pin 21, D1 with pin 22, ..., D7 with pin 28. That's all.
Now you can plug in the interface in the CPC. Switch the power on. If the CPC doesn't work normal please switch the power off and you have to watch for faults in the connection of your interface :-(. If everything is ok then you have to copy the assembler code and do the next test.
'''Bugs and Confusing things in the GIF schematic:'''
* Confusing: Signals 0..15 on the left side of the schematic refer to address lines A0..A15
* Bug: Z80-STI Pin 3 (TCO) should be wired to Pin 39 (RC), not to Pin 34 (A1).
Second part: How to program the interface. (The assembler code is saved in RS232.ASM)
[[File:Rs232cpc.lzh]] - All info and files on topic
[[Category:Peripherals]]