- 2072 Kartik · 4 marks
RS-232A criteria for simplex/half/full duplex
Short answer
Simplex uses a one-way driver/receiver and GND. Half-duplex needs RTS/CTS for line turn-around, both ends with driver/receiver, and a master-slave protocol. Full-duplex has independent TX/RX with optional flow control. Common criteria: baud rate, ±3–15 V levels, under 15 m cable, and parity error detection.
What are the criteria which should be involved during the design of RS-232A in Simplex, Half Duplex and Full Duplex modes.
When designing an RS-232C link for simplex, half duplex or full duplex operation, the following criteria are considered.
| Criterion | Simplex | Half duplex | Full duplex |
|---|---|---|---|
| Direction of data | One way only | Both ways, one at a time | Both ways simultaneously |
| Signals/wires | TXD (one side), RXD (other), GND | TXD, RXD, GND plus RTS/CTS for line turn-around | TXD, RXD, GND (+ optional handshake) |
| Drivers and receivers | Driver at sender, receiver at receiver | Both ends have driver and receiver; direction control logic | Both ends have independent driver and receiver |
| Handshake | Not required (or one-way DSR) | Required: RTS/CTS to claim the channel | Optional hardware flow control |
| Protocol / software | Simple, no reply | Needs master-slave or token protocol to avoid collision | Independent transmit/receive tasks, buffers |
| UART | TX or RX only | TX and RX, but not used together | TX and RX used independently |
| Throughput | Lowest | Medium | Highest |
| Example | Computer to display board | Polled instrument network | PC to modem |
Common design criteria
- Baud rate (up to 20 kbps) agreed by both ends, with same data bits, parity and stop bits.
- Voltage levels: +/-3 to +/-15 V; use MAX232/MAX3232 for TTL conversion.
- Cable length (about 15 m, load capacitance below 2500 pF) and shielding to reduce noise.
- Connector and pin assignment (DB-9/DB-25, DTE/DCE; null modem if DTE-DTE).
- Common ground between both devices.
- Flow control (RTS/CTS, DTR/DSR or XON/XOFF) and buffers in half and full duplex.
- Error detection with parity and error handling (framing, overrun).
✓ Answer checked by Claude Sonnet 5.5
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