CN0416-用戶指南Wiki

2512788 2021-03-23 | pdf | 444.24KB | 次下載 | 3積分

資料介紹

This version (03 Jan 2021 21:57) was approved by Robin Getz.The Previously approved version (17 Jul 2019 01:26) is available.

EVAL-CN0416-ARDZ Shield Overview
- RS-485 Communications
- Schematic, PCB Layout, Bill of Materials

EVAL-CN0416-ARDZ Shield Overview

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.

RS-485 Communications

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.

Switch	Function
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

Summary of Switch Configurations

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
RS-485 Configuration	S2	S4	S5	S6	S7
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

Isolated vs Non-Isolated RS-485 Operation

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

Full Duplex or Half Duplex Operation

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)

When S4 and S5 are in switch position 1, S2 MUST be placed in switch position 1 or 4, depending on the part you are using.
When S4 and S5 are in switch position 2, S2 MUST be placed in switch position 2 or 3, depending on the part you are using.

Cable Length and Termination Selection

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

When S6 and S7 are in switch position 1, there is no RS-485 termination. This is suitable for low-power, short transmissions over a total distance less than 0.78 m.
When S6 and S7 are in switch position 2, a parallel resistance termination is inserted. This is suitable for long distance, high power transmissions not exceeding a total distance of 4000 ft.

Hex Switch Addressing

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)
0	Low	Low	Low	Low
1	Low	Low	Low	High
2	Low	Low	High	Low
3	Low	Low	High	High
4	Low	High	Low	Low
5	Low	High	Low	High
6	Low	High	High	Low
7	Low	High	High	High
8	High	Low	Low	Low
9	High	Low	Low	High
A	High	Low	High	Low
B	High	Low	High	High
C	High	High	Low	Low
D	High	High	Low	High
E	High	High	High	Low
F	High	High	High	High

RJ-45 Connection and Wiring Multi-Node Systems

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.

With a straight-through connection, the CAT5 cable should connect two boards using the same port, e.g. (P4 of a master node is connected to P4 of a slave node in isolated communications).

With a crossover connection, the CAT5 cable should connect two boards using opposite ports, e.g. (P6 of a master node is connected to P24 of a slave node in non-isolated communications).

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

ADALM-UARTJTAG Connection

The CN0416 has a 10 pin 5×2 connector to interface with an ADALM-UARTJTAG. The yellow LED DS2 will indicate a live connection between the two devices.