It works on half-duplex communication to implement the function of converting the TTL level into RS-485 level which means it can either transmit or receive at any time, not both, it can achieve a maximum transmission rate of 2.5Mbps. MAX485 transceiver draws a supply current of between 120μA and 500μA under the unloaded or fully loaded conditions when the driver is disabled. If the /SS pin of the master is an input and if a low input level is detected, the processor sets the MODF bit in the SPI status register a "mode fault" condition. For the QScreen, /SS is not used for SPI communication because it is used to control the direction of the RS485 transceiver; you can use any digital I/O line as a /SS signal. If the 68HC11 is initialized as a master by setting the MSTR bit, then bit 5 of the Port D data direction register (PORTD.DIRECTION) determines whether /SS is an input or an output.
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. There is no standard connector for the protocol. There are nonelectrical considerations to determine how many devices you put on an MSTP network. Unit identifier is used with Modbus TCP devices that are composites of several Modbus devices, e.g. Modbus TCP to Modbus RTU gateways. Our advice: For longer networks with lots of devices, choose 38k400 baud over 76k800 baud and optimize using COV, separate networks and by setting the Max Master to a lower number. If they quote a number such a 100Ohms you have a good cable. 70 as a best case and 100 as a worst case (obviously reading descriptions will take more) multiply by the number of objects and properties you are going to poll on a regular basis. So take advantage of that and let your systems MCUs implement heart beat handshaking directly though the RS485 communications layer using appropriately designed small packets. 4. Take care where you run your cables. Choose low capacitance cables.
It seems obvious not to wind your cable around other cables or sources of electricity/magnetism. For example, at 115k baud your cable should not be much longer than 2500 feet. Although the maximum standard baud rate of the primary serial port is 19200 baud, what is rs485 cable nonstandard baud rates of over 80 Kbaud can be attained by the 68HC11's on-chip UART and the onboard RS232 driver. These standard 9-pin serial connectors are located on the top edge of the QVGA Controller. Some cables are designed so that the impedance is relatively independent of distance. If they quote an impedance per meter/foot you have chosen the wrong kind. A clue to knowing if you selected one is to look at the cables Nominal Impedance. You want one of these cables. We recommend these two cables. The two values provide a sufficient margin for a reliable data transmission even under severe signal degradation across the cable and connectors. Look for UL on the data sheet. Be sure to use a wire pair such as the blue and blue/white pair for the data lines and a third wire or pair twisted together for the common connection.
However, the higher the baud rate the more sensitive the cable is to the quality of installation issues like how much twisted pair is unwound at each termination start to become very very important. This converter converts a USB port to not only RS485 but also RS232 and TTL, making it more versatile. Typing a carriage return at the terminal should now produce the familiar "ok" response via the Serial2 port. Wrong in the sense to determine the value of terminating resistors now requires measurements and calculations. In fact, the program works the same as it did before, but now it is using the secondary serial port instead of the primary port -- and you didn’t even have to recompile the code! They have Shielding Jacket over the insulation layer to protect against the Electromagnetic Interference and also each pair of wires is twisted together to prevent any current loop formation and thus much better protection against the noise. Yes. Use one pair for Tx, Rx and a conductor from another pair for the ground reference signal. The twisted pair used for Tx and Rx is more effective at noise cancellation than the shield.