java中使用modbusTcp与plc通信

本人只是用此协议写过上位机，所以这里介绍的只是在java中的一些使用

首先引入jar包

    <dependency><groupId>com.intelligt.modbus</groupId><artifactId>jlibmodbus</artifactId><version>1.2.9.7</version></dependency>

下面是自己封装的统一连接类

@Data
@Slf4j
public class ModBusConnector {private static final Map<InetAddress, ModBusConnector> connectorMap = new HashMap<>();private static final int MOD_BUS_PORT = 502;private static final int SERVER_ADDRESS = 1;private static final boolean KEEP_ALIVE = true;private final ModbusMaster modbusMaster;private final InetAddress ip;protected ModBusConnector(ModbusMaster modbusMaster,InetAddress ip) {this.modbusMaster = modbusMaster;this.ip = ip;}public static ModBusConnector fetchOrCreate(InetAddress ip, int timeout) {ModBusConnector connector = connectorMap.get(ip);if (connector == null) {ModbusMaster masterTCP = ModbusMasterFactory.createModbusMasterTCP(new TcpParameters(ip, MOD_BUS_PORT, KEEP_ALIVE));connector = new ModBusConnector(masterTCP, ip);}log.info("ModBus connector connecting: {}", connector);connector.getModbusMaster().setResponseTimeout(timeout);try {connector.getModbusMaster().connect();log.info("ModBus connector connected: {}", connector);} catch (ModbusIOException e) {throw new IllegalStateException(e+ip.getHostAddress());}return connector;}public static ModBusConnector fetchOrCreate(InetAddress ip) {return fetchOrCreate(ip, 3000);}public ReadHoldingRegistersResponse readRegisters(PlcReadRequest readRequest) {return WrappingUtil.runWithRetry(() -> {final long sending = System.currentTimeMillis();
//                log.debug("sending modbus read request: " +
//                        "waiting consume {}ms, ip={}, request={}", (sending - wait), ip, readRequest);ModbusRequest request;synchronized (modbusMaster) {try {if (!modbusMaster.isConnected()) {modbusMaster.connect();}request = ModbusRequestBuilder.getInstance().buildReadHoldingRegisters(SERVER_ADDRESS,readRequest.getStartAddress(),readRequest.getQuantity());final ReadHoldingRegistersResponse response = (ReadHoldingRegistersResponse) modbusMaster.processRequest(request);if (response.isException()) {throw new IllegalStateException("ModBus返回异常：" + response.getModbusExceptionCode());}final long sent = System.currentTimeMillis();log.debug("Successfully sent modbus read request : " +"sending consume {}ms, ip={}, request={}, response: {}",(sent - sending),ip,readRequest,response.getHoldingRegisters().getRegisters());return response;} catch (Exception e) {if (isConnected()) {disconnect();}throw new IllegalStateException(e);}}}, PlcConfig.getRetryTimes(),new IllegalStateException("failed refresh rgv status"+ip.getHostAddress()));}public void writeRegisters(PlcWriteRequest writeRequest) {WrappingUtil.runWithRetry (() -> {final long wait = System.currentTimeMillis ();final long sending = System.currentTimeMillis ();log.debug ("sending modbus write request: " +"waiting consume {}ms, ip={}, request={}", (sending - wait), ip, writeRequest);ModbusRequest request;synchronized (modbusMaster) {try {if (!modbusMaster.isConnected()) {modbusMaster.connect();}request = ModbusRequestBuilder.getInstance().buildWriteMultipleRegisters(SERVER_ADDRESS,writeRequest.getStartAddress(),writeRequest.getRegisters());ModbusResponse response = modbusMaster.processRequest(request);final long sent = System.currentTimeMillis();log.info("successfully sent modbus write request : time={}" +"sending consume {}ms, ip={},  request={}, response: {}",System.currentTimeMillis(),(sent - sending),ip,writeRequest,response.getModbusExceptionCode());} catch (Exception e) {if (isConnected()) {disconnect();}throw new IllegalStateException(e);}}}, PlcConfig.getRetryTimes (),new IllegalStateException("failed send command rgv status"+ip.getHostAddress()));}public boolean isConnected() {return modbusMaster.isConnected();}public void disconnect() {if (modbusMaster != null) {if (!modbusMaster.isConnected()) {log.info("connection already disconnected {}",this);} else {try {modbusMaster.disconnect();} catch (ModbusIOException e) {log.info("modbus disconnected false: {}",this,e);throw new IllegalStateException(e);}log.info("modbus disconnected success: {}",this);}}}}

代码快中用到了自己封装的工具类会放在文章结尾，这里截图解释以下关键部分

建立连接

读请求

写请求

关键理解

java中每个 int 是 4个字节 32位，但是寄存器中int数据类型是 16 位，而一个int类型就是寄存器中的一个地址位。
好比我想在 寄存器的第2个地址位的倒数第2个bit位写入 1，那么java中构建的就是
int [2] = new int[2]
int[1] = 1<<2//第几个bit位就要向前移几位
注意，此时随在第二个地址位写了 数值 2，但是由于java中int默认值是0，所以这样构建还会把第一个地址位数据置0，所以如果不想影响到第一个地址为数值，需要如下构建
int [1] = new int[1]
int[0] = 1<<2//第几个bit位就要向前移几位
此时下发时起始地址为要携程 1，不能再是 0

还有一点要注意的，一个plc中一个int如果只用了 8 个bit位，那么这 8个bit位是 16位中的高8位，即先高8位后低8位。