🔍 Key Concepts

• Inmarsat-C equipment interfaces and how they connect to external devices • Differences between DCE (Data Circuit-terminating Equipment) and DTE (Data Terminal Equipment) in an EIA-232/RS-232 connection • What a null modem cable does compared with a standard modem (straight-through) cable

💭 Think About

• For each option, ask yourself: would this setting or condition completely block data transfer, or would it more likely just cause errors or require matching settings? • Think about the role of parity bits and stop bits in serial communications: if they are set ‘incorrectly’, does that absolutely prevent communication, or can devices still sometimes talk if they match each other? • Consider which pin and wiring arrangement in an EIA-232 connector is responsible for the signal reference (ground) and which are responsible for transmit/receive paths.

✅ Before You Answer

• Identify which connector pin on a standard EIA-232 DB-25/DB-9 is signal ground and what happens if it is grounded as designed. • Review what a null modem cable is wired to do (which pins are crossed vs straight-through) and whether Inmarsat-C expects a DTE-to-DCE or DTE-to-DTE style connection. • Confirm whether mismatched or unusual parity/stop bit configurations will absolutely prevent any communication, or just require both sides to use the same settings.