RS485 Modbus RTU Interfaces
The CONV-USBTORS232/485 module derives the power from the USB port and doesn’t need any power adapter. The USB to RS485 Converter is a cost-effective module for transfer serial data over USB. USB to RS485 Converter ใช้ต่อกับ USB port ของ PC หรือ Note Book แปลงเป็นสัญญาณ RS485 Communication. When used as a converter, the master RS232 port provides bi-directional serial conversion to the 8 RS485 distribution ports. RS232, RS422, RS423 and RS485 are serial communication methods for computers and devices. Making effective use of serial devices often involves converting between RS232, RS485, and USB signals. The RS485 and RS232 serial communication protocols have been in use for over 50 years and are still widely used throughout business and industry. Devices using the RS232 protocol are limited to a distance of 15 meters between transmitter and receiver while still achieving the maximum data transmission rate.
The value given typically must be multiplied by the speed of light (c) to obtain units of meters per second. If termination is required in a system, the termination impedance value should match the Characteristic Impedance of the cable. Characteristic Impedance (Ohms): A value based on the inherent conductance, resistance, capacitance and inductance of a cable that represents the impedance of an infinitely long cable. When choosing a transmission line for RS-485, it is necessary to examine the required distance of the cable and the data rate of the system. A byproduct of the differential voltage system is the extended data transfer distance, increased transmission speed, and lower voltage use seen with RS485. RS485 is the most versatile communication standard in the standard series defined by the EIA, as it performs well on all four points. Any standard communications software for your RS-232 serial ports will work. When the cable is cut to any length and terminated with this Characteristic Impedance, measurements of the cable will be identical to values obtained from the infinite length cable. That is to say that the termination of the cable with this impedance gives the cable the appearance of being infinite length, allowing no reflections of the transmitted signal.
So that’s how converter rs485 being used. The termination also includes pull up and pull down resistors to establish fail-safe bias for each data wire for the case when the lines are not being driven by any device. Layer two of the OSI model includes the bit and framing protocol, which is outside of these EIA/TIA standards. Standard Parking Management System composed of the basic bit computer. RS485 meets the requirements for a truly multi-point communications network, RS485 standard and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus. RS485 Bias : 680 Ohm pull-up and pull-down (Jumper selectable). RS485 Termination : 120 Ohm (Jumper selectable). 230.4 Kbps. When cascaded, this drive capability provides the means to form very large RS485 systems using “Star or Home Run” configurations. The following table provides an overview of the two standards. Standards have been developed to insure compatibility between units provided by different manufacturers, and to allow for reasonable success in transferring data over specified distances and/or data rates. It does not mean that this protocol is part of the standards or that only this protocol may be used with the 232/422/485 standards. The RS232 may be converted to RS485 with a simple interface converter – it can have optical isolation and surge suppression.
The annex also says that certain applications may cause the resistor to fail so the installation must allow access for inspection and replacement. Several volts difference in the ground level of the RS485 transmitter and receiver does not cause any problems. The USB to RS485 Converter is designed to make serial port expansion quick and simple. Disable the RS485 hardware port. The desktop is connected to earth ground and the RS-485 port is referenced to the earth ground. This is partly due to hardware manufacturers’ concentration on providing USB connectivity rather than serial ports on laptop and desktop machines. To solve the “data collision” problem often present in multi-drop networks hardware units (converters, repeaters, micro-processor controls) can be constructed to remain in a receive mode until they are ready to transmit data. R E Smith, Inc. engineers and manufactures a comprehensive line of isolated and non-isolated converters, repeaters, multiport repeater hubs, fiber optic based products, and I/O boards. Sig- line. The RS485 receiver compares the voltage difference between both lines, instead of the absolute voltage level on a signal line.
