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

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Many cable manufacturers can recommend a 120 Ω cable intended to work with RS-422 or RS-485. It was originally referred to as EIA RS-485 in 1983, although it was implemented much later in 1998. It was designed to overcome the challenges of RS-422 and RS 232. This standard enables a data transfer rate of 10 Mbps up to 50 feet distance and can be easily extended to 4000 feet at a speed of 100 kbps. But, the RS-232 standard allows for synchronous communications, which is not compatible with the IBM PC serial port, as well as asynchronous communications, which can be. Additionally, data can be transmitted at up to 10MBit/s which is faster than most standards. As soon as U1 pulls the U9 enable line low, U9 latches the output data so that it stays constant until the next output data update. If you do, then U6 and U8 both fight to control the RX line resulting in faulty operation and possible IC damage. RS-485 discusses that it is used for devices up to 10Mbit/S, then says they need not be limited to 10Mbps. It also states that "the upper bound is beyond the scope of this Standard".

VERSITRON is a popular manufacturer of RS-485 standard devices such as 4 channel phone kits with RS485 data transmission capabilities, RS-485 2-wire telephone modems, and other products that have been used in high-speed telecommunication systems globally. However, I have included RN12 for two reasons: it is required for the current-sourcing option and keeping it in place for the current-sinking option assists debugging by allowing easy determination of whether an output line failure is within the latch or the output transistor. Software is used to define the latch output, and therefore we have total control of the load’s operation. You should NEVER have U6 and U7 installed if you have U8 installed and vice versa. 0.2V the receivers output switches to a 1 and when the voltage goes below -0.2V the receivers output switches to a 0. (or vice versa if there is inversion on the receiver) Since the last bit from a UART will be the stop bit (1), then the transmitter is turned off (the differential voltage goes to 0V, but not having gone less than -0.2V), this should leave the receiver with a 1 being output to the receiving UART.

When the C/MRI application software, resident in the PC, requests that a given SMINI node send the railroad data to be received as inputs on its 3 input ports, the U1 gathers the data, converts it to serial format, then activates U7’s DE enable line, which then seizes the serial bus for sending the input data to the PC. This is accomplished by using RC5, Pin 24, as a transmit enable line connected to U7’s driver enable (DE) input. Using the 100Ω resistor, this current is 5V (the normal charge on the capacitor) divided by 100Ω or 50mA. Therefore, you would not want to drive this level of filtering if you are using TTL circuits in your external hardware to switch input lines to ground. This way only one device, the driver IC on the RS485 card, is in command of the two transmit lines. The provided diagram illustrates the equivalent output schematic of the RS485 driver. In other words, to make the symbol match the waveform, the input to the schematic symbol would have to be reversed or inverted at the input to the symbol.

For the system to work, only the transmitter IC from one SMINI can be allowed to seize, i.e. transmit over, the bus at any one time and all other SMINI cards must have their U7 ICs held in their high impedance (open circuited) states. Ultimately, RS485 standard it can be thought of in a way that serial communication is more made for this usage as compared to the common USB and ethernet. Looking at RC5, Pin 24, the Transmit Enable (TXEN) line, this is a little more complicated. 3V, and when a binary 1 is being transmitted, the voltage must be more negative than -3V. This is typically handled by the protocol being used on top of RS-485, such as Modbus or Profibus.For example, in a Modbus network, each message sent by the master starts with the address of the device it’s intended for. RS485 drivers automatically return to their high impedance tri-state within a few microseconds after the data has been sent. The driver has the capability of driving 10 receivers of 4k impedance, but the actual number that can be driven depend on the actual input impedance of the receivers, bit rate, wire, stub lengths, biasing and termination of the network.