RS - 232 and RS - 485 are both serial communication standards, and their most essential differences are as follows:
1. Electrical Characteristics
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RS - 232
- It uses single - ended signaling. The voltage levels for a logic 0 and a logic 1 are relatively large. For example, a logic 0 is typically represented by a voltage between +3V and + 15V, and a logic 1 is between - 3V and - 15V. The large voltage swings mean that the signal is more susceptible to electrical noise and interference. Also, the maximum cable length for RS - 232 is usually limited to around 15 meters due to signal attenuation and distortion at longer distances.
- The transmitter and receiver use different signal lines and a common ground. The ground reference is critical, and any potential difference between the grounds of the transmitting and receiving devices can lead to signal errors.
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RS - 485
- RS - 485 uses differential signaling. It defines two wires, A and B. The difference in voltage between these two wires determines the logic level. A voltage difference greater than +200mV between A and B represents a logic 1, and a voltage difference less than - 200mV represents a logic 0. This differential signaling provides better noise immunity compared to RS - 232.
- The maximum cable length can be much longer, up to 1200 meters (depending on factors such as cable type and data rate). The differential signal allows for reliable communication over longer distances because the common - mode noise (noise that affects both wires in the same way) is largely cancelled out.
2. Network Topology and Device Connectivity
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RS - 232
- It is typically a point - to - point communication standard. That is, it is mainly used to connect two devices directly, such as a computer and a modem or a computer and a single serial device. It does not support multi - drop configurations easily. Each connection usually requires a separate RS - 232 port on the host device.
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RS - 485
- RS - 485 supports multi - drop configurations. Multiple devices (up to 32 devices per bus segment in some cases) can be connected to the same RS - 485 bus. This makes it suitable for applications where several devices need to communicate with a central controller, such as in industrial automation systems where multiple sensors and actuators communicate with a programmable logic controller (PLC).
3. Data Transfer Rates
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RS - 232
- The data transfer rate is relatively limited. The maximum data rate for RS - 232 is usually around 20 kbps, although higher speeds are possible in some cases. This speed is sufficient for many simple serial communication applications such as connecting an old - style serial mouse or a simple serial console.
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RS - 485
- RS - 485 can support much higher data transfer rates. It can handle data rates up to 10 Mbps or even higher in some configurations. This high - speed capability makes it suitable for applications that require fast data transfer, such as real - time data acquisition in industrial settings or high - speed communication between multiple intelligent devices.