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RS-485 and RS-232 Communication Interface Guide
1. Introduction
RS-485 and RS-232 are serial communication interface standards commonly used in industrial applications for data transmission between devices. They serve as "transmission channels" enabling reliable data exchange between different devices.
1.1 Key Features Comparison
| Feature | RS-485 | RS-232 |
|---|---|---|
| Transmission Mode | Differential Signal | Single-ended Signal |
| Maximum Devices | 32 (expandable to 256) | Point-to-point (2) |
| Maximum Distance | 1200 meters | 15 meters |
| Maximum Baud Rate | 10Mbps | 20Kbps |
| Noise Immunity | Strong | Weak |
| Common Applications | Industrial Fieldbus | Short-distance Connection |
2. Working Principle
2.1 RS-485 Principle
- Uses differential signal transmission
- Data transmission via A(+) and B(-) lines
- Signal determination:
- VA - VB > +200mV represents logic "1"
- VA - VB < -200mV represents logic "0"
2.2 RS-232 Principle
- Uses single-ended signal transmission
- Data transmission via TXD(transmit) and RXD(receive)
- Signal levels:
- +3V to +15V represents logic "0"
- -3V to -15V represents logic "1"
3. Wiring Guide
3.1 RS-485 Wiring
Basic connections:
- A(+): Positive differential signal line
- B(-): Negative differential signal line
- GND: Signal ground (recommended)
IMPORTANT For long-distance transmission, 120Ω termination resistors should be added at both ends to prevent signal reflection.
3.2 RS-232 Wiring
Minimum connections:
- TXD: Transmit Data
- RXD: Receive Data
- GND: Signal Ground
Full connections include:
- RTS: Request to Send
- CTS: Clear to Send
- DTR: Data Terminal Ready
- DSR: Data Set Ready
4. Common Applications
4.1 RS-485 Applications
- Industrial fieldbus systems
- Smart building control
- Security monitoring systems
4.2 RS-232 Applications
- Industrial equipment debugging
- Serial printer connection
- Computer peripheral connection
5. Troubleshooting
- Unstable Communication:
- Check wiring connections
- Verify baud rate settings
- Confirm signal ground connection
- Check termination resistors (RS-485)
- Data Errors:
- Check signal polarity (RS-485)
- Verify communication parameters
- Confirm cable quality
6. Selection Guidelines
- RS-485 Suitable Scenarios:
- Multi-point communication needed
- Long-distance transmission
- Strong environmental interference
- High reliability required
- RS-232 Suitable Scenarios:
- Point-to-point short distance communication
- Device debugging
- Simple connection cases