The part number "SN65HVD1785DR" is a product manufactured by Texas Instruments (TI). It is a transceiver designed for the RS-485/RS-422 serial communication standards, primarily used for differential bus communications. This device is a half-duplex transceiver with low Power consumption and is used in industrial applications, such as motor control and fieldbus networks.
Here is the detailed explanation, along with the pin function specifications and circuit principle, including the package type and pinout list:
Package Type:
The SN65HVD1785DR comes in a SOIC-8 (Small Outline Integrated Circuit - 8 pins) package.Pinout Description:
Pin Number Pin Name Function Description 1 A RS-485 Differential Input/Output Pin: This pin is used for the differential signal that is transmitted or received over the RS-485 bus. It is the positive signal line in a differential pair. 2 B RS-485 Differential Input/Output Pin: This pin is the negative signal line in the RS-485 differential pair. The voltage difference between pins A and B is used to interpret the data. 3 DE Driver Enable Pin: This pin controls the transmission driver. When DE is high, the driver is enabled, and the device transmits on the A and B lines. When DE is low, the driver is disabled, and the receiver is active. 4 RE Receiver Enable Pin: This pin enables or disables the receiver. When RE is low, the receiver is enabled and can receive data from the A and B lines. When RE is high, the receiver is disabled. 5 RO Receiver Output Pin: This pin provides the received data. The receiver outputs a logic high or low signal corresponding to the differential voltage on pins A and B. 6 Vcc Power Supply Pin: This pin provides the power supply for the device. The recommended operating voltage is typically +5V. 7 GND Ground Pin: This pin is connected to the ground of the system to complete the circuit. 8 NC No Connect: This pin is not connected internally and can be left floating. It has no specific function in the circuit.Pin Function Description (Detailed List)
Pin 1 (A): This pin is the positive voltage line of the differential bus in an RS-485 network. It carries the differential signal, which is used to transmit data between nodes. The voltage at this pin is compared with the voltage at Pin 2 (B) to interpret the data being transferred.
Pin 2 (B): This pin is the negative voltage line of the differential bus. Together with Pin 1 (A), it forms a differential pair that allows the transceiver to transmit and receive data. The voltage difference between these pins determines the logic state.
Pin 3 (DE): This pin is used to enable or disable the driver section of the transceiver. When DE is high, the transmitter is active, and it can send signals through Pins A and B. If DE is low, the driver is turned off, and the receiver can operate.
Pin 4 (RE): The RE pin enables or disables the receiver functionality. A low logic level on RE enables the receiver to monitor the A and B lines, while a high logic level disables the receiver. In a typical application, RE is tied low to keep the receiver active.
Pin 5 (RO): The RO pin provides the output of the receiver section. The voltage at this pin corresponds to the received data, and it will be a logic high or low, depending on the differential voltage received on Pins A and B.
Pin 6 (Vcc): This pin connects to the power supply of the device. The voltage at this pin should typically be 5V (±10%) to ensure proper operation of the transceiver.
Pin 7 (GND): This pin is the ground reference for the device. It provides a return path for the current and should be connected to the common ground of the system.
Pin 8 (NC): This pin is not internally connected and has no function in the circuit. It is typically left unconnected but should not be used for any other purpose in the design.
20 FAQ About the SN65HVD1785DR
Q: What is the function of the DE pin on the SN65HVD1785DR? A: The DE pin is used to enable or disable the driver. When DE is high, the driver is active, and the device transmits data over the RS-485 bus.
Q: Can I use the SN65HVD1785DR in a 3.3V system? A: The SN65HVD1785DR is designed for a 5V power supply, so operating it at 3.3V is not recommended.
Q: What is the maximum data rate of the SN65HVD1785DR? A: The maximum data rate for the SN65HVD1785DR is typically 20 Mbps, making it suitable for high-speed data communication.
Q: How does the SN65HVD1785DR handle differential signaling? A: The device uses differential signaling on the A and B pins, where the voltage difference between these pins determines the logic level of the transmitted or received signal.
Q: What happens if I leave the RE pin high? A: If the RE pin is high, the receiver section is disabled, and the device cannot receive data from the RS-485 bus.
Q: How do I connect the SN65HVD1785DR in a network? A: The SN65HVD1785DR is typically connected in a multi-drop bus configuration with other RS-485 transceivers, with proper termination resistors at both ends of the bus.
Q: What is the significance of the RO pin? A: The RO pin outputs the received data from the A and B pins, representing the logic state of the differential signal.
Q: Can the SN65HVD1785DR drive long cable distances? A: Yes, the device is designed for long-distance communication, typically supporting distances up to 4000 feet at lower data rates.
Q: What is the recommended termination for the RS-485 bus? A: The RS-485 bus should be terminated with a resistor of around 120Ω at each end of the bus to prevent signal reflections and ensure reliable communication.
Q: Is the SN65HVD1785DR suitable for industrial applications? A: Yes, the SN65HVD1785DR is widely used in industrial communication systems, such as factory automation and fieldbus networks.
Q: How do I ensure the proper voltage levels for the SN65HVD1785DR? A: The device requires a 5V power supply (±10%), and the A and B pins should experience voltage levels that are within the RS-485 differential specification.
Q: Can I use the SN65HVD1785DR in a 2-wire configuration? A: Yes, the SN65HVD1785DR can be used in a 2-wire half-duplex configuration, where data is transmitted and received on the same two wires.
Q: What is the purpose of the NC pin? A: The NC pin is not connected internally and serves no functional purpose in the circuit. It can be left floating.
Q: What is the input impedance of the SN65HVD1785DR? A: The device has a high impedance on the A and B pins when the driver is disabled, allowing multiple devices to share the bus without interference.
Q: Can the SN65HVD1785DR operate in a 4-wire full-duplex mode? A: The SN65HVD1785DR is designed for half-duplex operation, meaning it can either transmit or receive at any given time, but not both simultaneously.
Q: Does the SN65HVD1785DR support hot-swapping? A: The device is capable of hot-swapping, but care should be taken to avoid damage from improper voltages or signal levels during insertion.
Q: How do I protect the SN65HVD1785DR from ESD? A: ESD protection can be implemented with external diodes or resistors on the A and B pins, ensuring they are within safe operating limits during voltage spikes.
Q: How do I troubleshoot a communication issue with the SN65HVD1785DR? A: Ensure the DE and RE pins are configured correctly for transmission and reception, check the power supply voltage, and verify that the differential signal on A and B is within the acceptable range.
Q: Can I use the SN65HVD1785DR in a multi-master setup? A: Yes, the SN65HVD1785DR can be used in a multi-master setup, but proper bus arbitration must be employed to avoid data collision.
Q: What is the recommended maximum bus length for the SN65HVD1785DR at 10 Mbps? A: At 10 Mbps, the recommended bus length is approximately 1000 meters, depending on the quality of the cable and termination.
This completes the detailed explanation of the SN65HVD1785DR and its pinout, as well as the FAQ section.