Super Mini-Node Interface Card (SMINI) - Part 1

EIA-485, also known as TIA/EIA-485 or RS-485, is a standard defining the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. There are many cables available meeting the recommendations of RS-422 and RS-485, made specifically for that application. 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. Data rate is usually the primary factor. The driver is in charge of filling this data structure from the values given by the device tree. Again the amount of loss depends of the values of the series and parallel resistance and the loss will increase with frequency. 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. Difference measurements (measuring Bus A vs. This difference in earth ground may be high enough to cause damage to the RS-485 devices, but connecting a third wire between their circuit commons/earth grounds would try to bypass the power earth common (this is often called a ground loop) causing excessive current in the third wire.

Conversely, the output that goes low when the input goes high is often called the "inverting" output. Systems with long lengths benefit from using low capacitance cable. Branching the cable to a receiver will cause secondary reflections which will cause more and unpredictable ringing of the signal. At node locations requiring more than 72 I/O lines, you can group SMINI cards together. A couple of disadvantages are that the network is being driven without data on it so contention is more likely, and software complexity increases. The RS-232 standard title is "Interface Between Data Terminal Equipment and Data Circuit Terminating Equipment Employing Serial Binary Data Interchange". When used as a converter, the master RS232 port provides bi-directional serial conversion to the 8 RS485 distribution ports. When used as a repeater, the master RS485 port provides bi-directional serial communications to the 8 RS485 distributation ports. Bias on the RS485 distribution ports is fixed to hold the port in idle mode if it is not being used, or is inactive. Jumpers allow the RS485 distribution port termination resistors, RS485 standard and the receive function to be disabled. Data received into a distribution port is not transmitted out any other distribution port.

RS485 communications. This data structure is used to set and configure RS485 parameters in the platform data and in ioctls. This standard is widely used for communications in industrial automation because it can be used effectively over long distances and in electrically noisy environments. DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units. This whole system allows manufacturing facilities to control their devices remotely and also set-up automation. RS-485 functions by defining the transmission of ‘0’s and ‘1’s via the positive or negative states of the transceiver terminals, A and B. To perceive the same logical state, all devices on the communication link must generate and detect signals of the same polarity.A reversed device will read and generate incorrect signals, leading to a communication breakdown. RS-485 stands out from other signaling standards due to its significant differential output voltage and extensive common-mode range.

All of the application guides and data sheets that say RS-485 has a limit of 1200 meters or 10Mbit are flat out wrong. It is optimal for outdoor use cases that need reliable data collected over years. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. In practice you will probably use 5% resistors. The RS485 drivers feature enhanced ESD performance, and our design employs 22 Ohm series protection resistors. The master RS485 port has jumper selectable bias and termination resistors. Fast auto turn-around, from transmit to receive mode, requires no software delays, no jumper settings, and thus eliminates timing problems and data collisions. The RS232 master port can be jumper configured as DTE or DCE. A true multi-point network consists of multiple drivers and receivers connected on a single bus, where any node can transmit or receive data. Once a requested data is sent the hardware reverts back into a receive mode. The SMINI card is designed so that each input line is wired from the external hardware directly into the appropriate pin on input buffers U3-U5.