SN65HVD230-based CAN bus transceiver and application of the principle
Abstract: SN65HVD230 is produced by Texas Instruments 3.3V CAN transceiver, the device suitable for high speed communication, good anti-interference capability and high reliability CAN bus serial communication. SN65HVD230 paper introduces the structure, principle and its application of intelligent power controller.
Introduction
CAN bus communication with its high speed, good resistance to electromagnetic interference, high-reliability serial communication can be realized, so in practical applications has a very high value. However, with the continuous development of integrated technology, in order to save power and reduce circuit size, some new CAN bus controller logic on average with LVTTL, which requires corresponding bus transceiver. TI produced SN65HVD230 circuits solves this problem.
SN65HVD230-based CAN bus transceiver and application of the principle
1 SN65HVD230 Introduction
SN65HVD230 is a Texas Instruments 3.3CAN bus transceiver, mainly with a CAN controller with the DSP TMS320Lx240x series supporting the use of the transceiver has differential ability to send and receive the maximum rate of up to 1Mb / s. Widely used in automotive, industrial automation, UPS control and other fields.
SN65HVD230-based CAN bus transceiver and application of the principle
1.1 Main features and pin functions
SN65HVD230 can be used in high interference environments. The device at different rates have a good ability to send and receive, its main features are as follows:
* Fully compatible with ISO11898 standards;
* High input impedance, allowing 120 nodes;
* Low current standby mode, typical current is 370μA;
* Signal transmission rate of up to 1Mb / s;
* With thermal protection, open circuit failure protection;
* Transient interference with the anti-protection function of the bus;
* Slope control to reduce radio frequency interference (RFI);
* Differential receiver with a wide range of common-mode anti-interference, electromagnetic interference (EMI) capabilities.
SN65HVD230-based CAN bus transceiver and application of the principle
SN65HVD230 by PSOP8 package, the specific pin arrangement and the logic function shown in Figure 1, Table 1 lists their pin functions.
Table 1 SN65HVD230 the pin function
Pin No. Pin Name Pin Function Description
1 D Enter CAN controller to send data input
2 GND to ground
3 Vcc 3V 3V supply voltage power supply
4 R output CAN bus receive data output
5 VREF Reference Voltage Reference Voltage Output
6 CANL CAN CAN bus low-low voltage input / output
7 CANH CAN CAN bus high-high-voltage input / output
8 Rs slope resistor input mode choice
1.2 mode, and control logic
SN65HVD230 high-speed, slope, and wait for the 3 different operating modes. The operating mode control can be achieved through the control pin Rs. Figure 2 is SN65HVD230 CAN bus system in the typical application diagram. As can be seen from the diagram, CAN controller's output pins Tx data input received SN65HVD230 D, this CAN node can send data to the CAN network; the CAN controller receives the pin Rx and SN65HVD230 data output R is connected, for receiving data. SN65HVD230 mode select port Rs one end grounded through the jumper and the slope resistor connection can be realized by means of hardware mode option 3, in which the slope is 0 ~ 100kΩ resistor potentiometer. VRs for the increase in the Rs pin voltage. The choice of specific models listed in Table 2.
Table 2 SN65HVD230 work mode choice
Vrs mode
VRs ≥ 0.75Vcc wait mode
10kΩ to 100kΩ ground slope control mode
VRs ≤ 1V high-speed mode
Rs connected to the logic low level can work in high-speed mode transceiver. In high-speed mode, the communication transceiver to the highest rate, at this time no internal output rise and fall slope limits, but in this mode, the maximum speed limit and the length of the cable.
In some occasions, taking into account issues such as system cost, the use of non-shielded cable, the transceiver must meet conditions, such as electromagnetic compatibility. In order to reduce the rapid increase in levels of electromagnetic interference caused, in SN65HVD230 slope control method is introduced. This control method can be connected to the Rs pin on the slope resistor in series to achieve. Voltage conversion and the slope of the relationship between resistance shown in Figure 2.
In the Rs pin with logic high (≥ 0.75Vcc), allows the device to enter standby mode, standby mode, the system only "hear" the message sent over. In the "listening" state, the sending transceiver functions in a shutdown state, the receiving function is still active. At this point, the receiver for the bus is always hidden.
1.3 Control Logic
SN65HVD230 use positive logic control, there are two ways to send and receive, the specific control logic as shown in Table 3.
Table 3 SN65HVD2304 control logic
Send receive
Input D Rs Rs differential input output bus state output R
CANH CANL
L XRs ≤ 1.2V H L dominant VIN ≥ 0.9V X L
H Z Z recessive 0.5V <VID <0.9V X?
Open X Z Z recessive VID ≤ 0.5V X H
X VRS ≥ 0.75Vcc Z Z recessive Open X H
Where, Z said high impedance state,? Said the uncertain state, X said nothing.
2 practice
An automatic test system requires multiple real-time controllable AC power supply, for which the author designed a CAN bus based intelligent power controller. The main computer system installed CAN bus communication control card, power supply controller with CAN bus communication adapter card, it can control the card and adapter cards to achieve the computer and the communication between the intelligent power controller to complete control of the power controller and power controller output state of each test.
2.1 System Principles
The power supply controller is SN65HVD230 based CAN bus transceiver and 3.3V Cygnal company with integrated CAN controller C8051F040 MCU to design the CAN controller and CAN bus communication bus communication adapter card. The block diagram shown in Figure 4, each network node through the PC control to achieve the specific control functions, and thus the composition of the network control system.
SN65HVD230-based CAN bus transceiver and application of the principle
2.2 CAN bus communication control card design
CAN control the entire network, CAN bus communication controller plays a very important role. The card includes C8051F040 MCU, dual-port RAM and the control circuit, interrupt application circuit, reset circuit, and CAN drive circuit. The block diagram of the controller shown in Figure 5. CAN communication controller of each node through the CAN bus will be linked together to a peer network into a simple "more than a master of" control network. PC via CAN bus communication control card to the network, each node has a different address to send the control command word in various formats, and representatives of the various network nodes, each node in the state of the data words read back, to assert control over the CAN network.
2.3 CAN Node
In the CAN control network, the network node is "from those" which by the appropriate address matching to identify the control card information sent. If the information is not sent to their own, not carry out any action, if the information is distributed to their own, then the node to receive information and perform the appropriate action. In the CAN control network, the information transmitted through the frame mode. CAN node set frame format according to content into the appropriate control procedures to control the operation of the external circuit. CAN bus system block diagram shown in Figure 6.
2.4 Design of mixed-level circuit interference
As the intelligent power controller itself is a mixed-level system, a number of road within the 220V/50Hz AC, 3.3V DC level control circuit, CAN network interface power control with different levels of equality, it signals the need to achieve different levels of isolation, to enhance the system's anti-jamming capability.
The system C8051F040 control signals through optical isolation and drive control relays after treatment in order to achieve the AC power output control, thereby ensuring high-power AC power supply and control circuit within the effective separation between. The CAN interface between the transceiver and the controller uses LVTTL / LVCMOS compatible to achieve high-speed optical isolation between the different levels of electrical isolation.
2.5 System Software
System Software primarily by the CAN bus communication control card control procedures and control procedures for each node in two parts. CAN bus communication control card control program is based on Windows programming, and is not to repeat, this paper gives the nodes of the control procedures.
SN65HVD230-based CAN bus transceiver and application of the principle
Various control functions mainly by calling the system's general function and performance function to achieve. Among them, the system universal function for system initialization and implementation of a number of common features. First initialize the CAN system, while the completion of the port configuration, bit of time to determine the message body configuration. The node initialization function as follows:
WDTCN = 0xde; / / off watch dog
WDTCN = 0xad;
config_IO (void); / / port configuration function, to achieve control module to control the distribution of pins
Clock (void); / / clock and bus speed CAN-defined functions
clear_msg_objects (void); / / clear the function of each message body
msg_objects_init (void); / / CAN message body initialization function
... ...
startCAN (); / / system allows for CAN communication
EA = 1; / / system open break;
SN65HVD230-based CAN bus transceiver and application of the principle
3 Conclusion
In practical engineering applications, SN65HVD230 as a new CAN bus transceivers with high speed and high resistance to electromagnetic interference, etc., together with its electrical connections is very simple, so it has good practicality.