CN0416 is an isolated and non-isolated RS-485 transceiver board which allows easy implementation of asynchronous serial (UART) data transmission between multiple Arduino form factor systems or nodes, especially over long distances. The circuit uses the ADM2682E RS-485 transceiver for isolated communications and the LTC2865 for non-isolated RS-485 communications. Both can be configured to either full-duplex or half duplex operation and with open or terminated transmission lines. The circuit has on-board RJ-45 ports which allows the use of the common CAT5 cable for fast physical wiring of nodes. The termination resistance is catered by default to the CAT5 cable characteristic impedance of 100 ohms but can be configured to support the standard RS485 cable impedance of 120 ohms. The cable also carries power supply lines which are by default unpowered but can be connected to a 3.3V supply from the board's low-dropout voltage regulator, ADP7102. The system has an on-board 10-pin connector compatible with the ADALM-UARTJTAG which allows for serial connections to a PC or other device.
The ADM2682E is capable of a data rate up to 16 Mbps and has true fail-safe receiver inputs with adjusted differential voltage threshold. It provides 5 kV signal isolation using the iCoupler data channel and 5 kV power isolation using the isoPower integrated dc-to-dc converter.
The LTC2865 is capable of a data rate up to 20 Mbps and has full fail-safe receiver inputs. An internal window comparator determines the fail-safe condition without the need to adjust the differential input voltage thresholds.
CN0416 can be configured to different settings and operations of the RS-485 communication standard using multiple on-board physical switches. There are three different switches to be configured for both isolated and non-isolated operations as shown below:
The switches shown in the image above provide the following functions.
|S1||Configures Address of RS-485 Node|
|S2||Selects Isolated vs non-Isolated Part and Half/Full Duplex Mode|
|S4||Selects Physical Layer Half/Full Duplex Mode of non-Isolated LTC2865|
|S5||Selects Physical Layer Half/Full Duplex Mode of Isolated ADM2682E|
|S6||Selects Termination Resistance of non-Isolated LTC2865|
|S7||Selects Termination Resistance of Isolated ADM2682E|
In summary, all switch positions for the configurable settings of the CN0416 in RS-485 communications are shown below. (Switch positions that do not matter for a setting are NA)
|RS-485 Configuration||Switch Positions|
|Isolated, Full Duplex, and Terminated||2||NA||2||NA||2|
|Isolated, Full Duplex, and Open||2||NA||2||NA||1|
|Isolated, Half Duplex, and Terminated||1||NA||1||NA||2|
|Isolated, Half Duplex, and Open||1||NA||1||NA||1|
|Non-Isolated, Full Duplex, and Terminated||3||2||NA||2||NA|
|Non-isolated, Full Duplex, and Open||3||2||NA||1||NA|
|Non-isolated, Half Duplex, and Terminated||4||1||NA||2||NA|
|Non-isolated, Half Duplex, and Open||4||1||NA||1||NA|
CN0416 can be configured to use either the ADM2682E or the LTC2865 for Half/Full Duplex RS-485 transmission. The difference between the part selected is that the ADM2682E provides complete signal and power isolation, where as the LTC2865 does not isolate the standard RS-485 transmission.
|Switch S2 Position||Duplex Mode||Operation||Part Used|
|Position 1||HALF Duplex (Isolated)||Signal and Power Isolated RS-485||ADM2682E|
|Position 2||FULL Duplex (Isolated)||Signal and Power Isolated RS-485||ADM2682E|
|Position 3||HALF Duplex (Non-Isolated)||Non-Isolated RS-485||LTC2865|
|Position 4||FULL Duplex (Non-Isolated)||Non-Isolated RS-485||LTC2865|
CN0416 can be configured to either full-duplex operation or half-duplex operation depending on the application. Switch S4 and S5 controls this setting with the differential RS-485 lines, and switch S2 controls the driver and receiver Enable.
|Mode||Operation||Switch Position Requirements|
|Isolated||Half-Duplex RS-485||S5 = Position 1 (HALF) & S2 = Position 1 (HALF ISO)|
|Full-Duplex RS-485||S5 = Position 2 (FULL) & S2 = Position 2 (FULL ISO)|
|Non-Isolated||Full-Duplex RS-485||S4 = Position 2 (FULL) & S2 = Position 3 (FULL NON_ISO)|
|Half-Duplex RS-485||S4 = Position 1 (HALF) & S2 = Position 4 (HALF NON_ISO)|
The data rate of RS-485 communications varies with the cable length. Below is a figure showing the relationship of data rate and cable length.
The type of termination also depends on the cable length as well as the cable characteristic impedance. The ordinary CAT5/CAT5E cable has a characteristic impedance of 100 ohms while the RS-485 standard cable has 120 ohms.
By default, the parallel termination resistance is 100 ohms which supports CAT5/CATE cables. But, this can be reconfigured to 120 ohms by disconnecting solder jumpers JP4, JP6, JP8 and, JP10 and shorting solder jumpers JP3, JP5, JP7, JP9.
Switch S6 and S7 controls the type of termination of the RS-485 lines.
|Mode||Switch S6 and S7 Position||Termination Type|
|Isolated||S7 = Position 1 (OPEN)||No Line Termination|
|S7 = Position 2 (TERM)||Parallel Resistance Termination|
|Non-Isolated||S6 = Position 1 (OPEN)||No Line Termination|
|S6 = Position 2 (TERM)||Parallel Resistance Termination|
The hex switch can be used to easily setup node addressing when the CN0416 is connected to a microcontroller via the Arduino headers. Bits are connected to analog inputs A0-A3 by default, which can be read as digital inputs by most Arduino platforms. Alternative bit mapping can be selected by resistor-stuff options on the CN0416, shown in parentheses. The bit values of the gpio pins used in node addressing are shown below.
|GPIO / Arduino Pin Connection|
|S1 Hex Switch Position||AIN0 (D7)||AIN1 (D6)||AIN2 (D5)||AIN3 (D4)|
The CN0416 has four RJ-45 ports, P4 and P5 for isolated communications and P6 and P24 for non-isolated communications. Each pair has a cross-over connection with each other. This facilitates the use of either a straight-through or crossover CAT5 cable.
Below shows illustrations of connecting multiple nodes using either a straight-through or a crossover cable for both isolated and non-isolated communications.
For Isolated Communications:
For Non-Isolated Communications
For half duplex set-ups, the ADALM-UARTJTAG needs to be setup for RS485 communications.
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