Super Mini-Node Interface Card (SMINI) - Part 1
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조회 3회 작성일 24-05-21 12:55
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Transmission and reception directions are defined from the perspective of the computer. We also see that the maximum allowed voltage levels for all interfaces are in the same range, but that the signal level is lower for the faster interfaces. We also see that there is a maximum slew rate defined for both RS232 and RS423. And that with an interface which does not require intelligent network hardware: the implementation on the software side is not much more difficult than with RS232. When using the default RS485 receivers with an input resistance of 12 kΩ it is possible to connect 32 devices to the network. The software simply checks to see that the input has remained stable for two or more samplings before it accepts any change in input. Looking at RC5, Pin 24, the Transmit Enable (TXEN) line, this is a little more complicated. 2) the GSM version also allows you to indicate a possible PIN (leave blank if there is no PIN) and the operator's APN (possibly you can search for it on Google).
Currently RS485 drivers are produced that can achieve a bit rate of 35 mbps. The maximum slew rate also limits the maximum communication speed on the line. This is, because on the other interfaces the communication channel is shared by multiple receivers and-in the case of RS485-by multiple senders. Currently available high-resistance RS485 inputs allow this number to be expanded to 256. RS485 repeaters are also available which make it possible to increase the number of nodes to several thousands, spanning multiple kilometers. RS485 is the only of the interfaces capable of internetworking multiple transmitters and receivers in the same network. Using RS-485, it is possible to construct a multi-point data communications network. Here the master initiates a communications request to a "slave node" by addressing that unit. Depending of the information in the sent data, zero or more nodes on the line respond to the master. Another approach is to design a 'single master' system. The emulation feature can be used to upgrade and replace other vendors’ gauges in OEM applications without changing system software. RS422 is a full-duplex system, meaning that a device using RS422 can send and receive information simultaneously.
The receiving device on each SMINI, the U6 receiver IC, has a high input impedance corresponding to a ¼ unit load. Default, all the senders on the RS485 bus are in tri-state with high impedance. RS485 drivers automatically return to their high impedance tri-state within a few microseconds after the data has been sent. First of all we see that the speed of the differential interfaces RS422 and RS485 is far superior to the single ended versions RS232 and RS423. RS232 has a separate communication line for transmitting and receiving which-with a well written protocol-allows higher effective data rates at the same bit rate than the other interfaces. Interesting is, that RS232 is the only interface capable of full duplex communication. Differential signals and twisting allows RS485 to communicate over much longer communication distances than achievable with RS232. With RS485 communication distances of 1200 m are possible. 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. The Electronics Industry Association (EIA) has produced standards for RS485, RS422, RS232, and RS423 that deal with data communications. RS485 was able to provide high speed data communications.
The RS485 standard is used when high speed serial data communications of 10 Mbps is needed. The Windows drivers are compatible with LabVIEW standard serial driver interface (NI VISA). There is no need for the senders to explicity turn the RS485 driver on or off. You do not need to understand electronics to build the SMINI. However, you may find situations where you need to connect the interface to external hardware that is prewired with a common ground and what you need to do is switch the hot, or power side, of the loads. Common standards: RS232 RS422 RS449 RS485 20 mA current loop RS485 was developed to provide high speed data. Therefore RS485 can overcome the practical communication speed limit of RS232. In a typical applications several address able devices may be linked to a single controlled (PC), and in this way a single line may be used for communication. It also keeps track of which information is data and which is address and determines when to activate each of the port enable lines for communication with the SMINI’s 9 different I/O ports - 3 for inputs and 6 for outputs. AD0 and AD1 are used to set the UART address.
