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

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The 8-lines of U1’s Port RD (Pins 19-22 and 27-30) are the bi-directional I/O data bus connecting U1 to the SMINI’s 3 input ports and 6 output ports. There is no wire shown connecting this third point between driver and receiver. There is a whole plethora of SenseCAP industrial-grade sensors, and this is just one of the many! This means that since only one transmission direction is available, only one device can send data. One of the factors limiting total cable length is the capacitive load. If you are pushing the data rate above 100kbit or the line length above 1000 meters, you may want to use a better grade of wire. If you have to know that it will work before you pull the cable, then get the required length of the cable and move the two devices next to each other, connect them and see if they can talk. Shunt Capacitance (pFft): The amount of equivalent capacitive load of the cable, typically listed in a per foot basis. In high quality cable, the conductor losses and the dielectric losses are on the same order of magnitude. As a general rule when the voltage measured (with respect to circuit common) is "high" the binary state is considered to be a 1 and when the voltage is low the state is 0. There are exceptions to this rule (such as differential logic and negative logic), but for the purpose of this discussion we'll talk about normal logic.

The RS485 protocol employs a differential voltage system that allows it to operate effectively in environments with higher levels of electrical noise. Single master systems (many other communications schemes are available) offer a straight forward and simple means of avoiding "data collisions" in a typical 2-wire, half-duplex, multi-drop system. It is NOT necessary to introduce long delays in a network to avoid "data collisions." Because delays are NOT required, networks can be constructed, that will utilize the data communications bandwidth with up to 100% through put. This implementation is very similar to a 4-wire RS-422 network. The RS-422 specification recommends 24AWG twisted pair cable with a shunt capacitance of 16 pF per foot and 100 ohm characteristic impedance. The cable has a maximum capacitance of 17 pF/ft (14.5 pF typical) and characteristic impedance of 100 ohms. 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. Systems with long lengths benefit from using low capacitance cable. Grounds between buildings may vary by a small voltage, but with very low impedance and hence the possibility of catastrophic currents - enough to melt signal cables, PCB traces, and transceiver devices.

And since a 120 Ω termination resistor can cause enough signal loss with an extremely long 120 Ω cable to stop the network from functioning, RS485 standard a 500 Ω or even a 1kΩ termination resistor may improve the signal quality enough without causing too much signal loss for the network to function. So why do you need to bias the network? This is why RS-485 states "The use of a cable termination is normally required".. RS-232 provides a list of circuits and says if you use a circuit; this is what it must do and it must be on this pin of the connector. User connections are compression screw terminal strips for the RS485 ports, an RJ11/12 telephone style connector for the RS232 port, and a 2.1mm barrel connector or 2 pin terminal strip for supply power. We are customer driven. Many of our products were developed and improved due to suggestions and feedback from our word-wide customer base.

Plenum cable is generally more expensive due to the sheathing material used. The annex of RS-485 states that "When employed, the shield shall be connected only to frame ground at either or both ends depending on the specific application." Shields usually have a lot more copper (and/or aluminum) than a single wire and can therefore carry a lot more current. 4.7 µF sets it to 350 ms. Again, the solenoids I have are more than happy with this. This means that 5 V inputs are be fine so as long as the input current doesn't exceed the maximum current rating (IIIK). For example, if the 877 wants to read data from Input Port A on Card 2 it activates the port enable line connected to the enable input on Input Buffer U3. This electrical noise can easily couple into the RS485 cabling to create data transmission errors. The RS485 drivers feature enhanced ESD performance, and our design employs 22 Ohm series protection resistors. Subsequently, OEM’s can reduce costs with a simplified loadlock design. From the perspective of previous C/MRI components the SMINI combines enhanced features of the original design Universal Serial Interface Card, the USIC, with two output cards and an input card, placing everything on a single board not much larger than the original USIC.