This post is divided in points, numbered for convenience as follows: FOREWORD BASICS KNOWN TUTORIALS PRINCIPLES DISCLAIMER and WARNING SERIAL Voltage and TTL levels GROUNDING LOOPBACK TESTS SPEED/DATA BITS/PARITY/STOP BITS/FLOW CONTROL CONVERTERS (or Data Cables) POWERING the converter (or data cable) Thanks and greetings go to ERRATA CORRIGE/additions Final words IMPORTANT EACH of them (with the only possible exceptions of points #12. and #13.) contains IMPORTANT information that may make the d