What is unit load in RS-485?
RS-485 specifies a hypothetical term of a unit load (UL), which represents a load impedance of approximately 12 kOhms. Drive capacity is 32 unit loads, i.e., 32 12kΩ receivers in parallel( gives 12k/32 = 375 Ohms). For receivers of higher input impedance, the number of unit loads on one bus can be higher.
What voltage does RS-485 use?
3V to 5.5V
RS485/RS422 Transceivers Operate from 3V to 5.5V Supplies and Withstand ±60V Faults.
How much maximum receivers are connects with RS-485?
RS485 meets the requirements for a truly multi-point communications network, and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus.
What is unit load in resistance?
A Unit Load (UL) is the input conductance of a receiver or transceiver (driver disabled) between either bus input terminal (A or B) and the device ground. A single unit load (1UL) is defined as a 1mA input current at an applied DC voltage of 12V, which is synonymous with a 12kΩ resistance, as shown in Figure 1.
What is a RS-485 cable?
RS-485 is an industrial specification that defines the electrical interface and physical layer for point-to-point communication of electrical devices. The RS-485 standard allows for long cabling distances in electrically noisy environments and can support multiple devices on the same bus.
Can you daisy chain RS485?
RS485 is Two-Way The sending device can be anywhere along the daisy-chain, and receiving devices can be on both sides of the sending device, so the signals have to travel both ways along the RS485 wire pair.
How many master devices can be on a single Modbus RS485 daisy chain?
two master devices
Their main feature is to allow two master devices to communicate to a single Modbus slave or to multiple Modbus slaves daisy-chained via RS-485. This is done as the illustration below shows.
Is RS485 a protocol?
RS-485 is still the most widely used protocol for POS, industrial, and telecom applications. The wide common-mode range enables data transmission over longer cable lengths and in noisy environments such as the floor of a factory.
How far can Rs-485 go?
4,000 feet
RS485 is popular for inexpensive local networks, multidrop communication links and long haul data transfer over distances of up to 4,000 feet. The use of a balanced line means RS485 has excellent noise rejection and is ideal for industrial and commercial applications.
What is Rs-485 used for?
What is RS-485? RS-485 is an industrial specification that defines the electrical interface and physical layer for point-to-point communication of electrical devices. The RS-485 standard allows for long cabling distances in electrically noisy environments and can support multiple devices on the same bus.
How many devices can be attached to a bus in RS485?
RS485 standard does not specify the maximum number of devices attached to a bus, but it does a lot of parameters that can be used for calculating this limit. Some of these parameters are: Low limit for bus resulting load resistance. Load (resistance) value that each device presents to the bus, called “Unit Load” (15 kΩ).
What is the difference between an RS-485 driver and a receiver?
RS-485 standard conformant drivers provide a differential output of a minimum 1.5 V across a 54-Ω load, whereas standard conformant receivers detect a differential input down to 200 mV. The two values provide a sufficient margin for a reliable data transmission even under severe signal degradation across the cable and connectors.
What are the applications of RS485 cable?
Applications. RS-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. It may be used to control video surveillance systems or to interconnect security control panels and devices such as access control card readers.
How is RS-485 used in industrial control systems?
Multiple receivers may be connected to such a network in a linear, multidrop bus. These characteristics make RS-485 useful in industrial control systems and similar applications. RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422.