public static void main(String argv[]) {
if (argv.length < 4) {
System.out.println("usage: java Modbus dns_name unit reg_no num_regs");
System.out.println("eg java Modbus aswales8.modicon.com 5 0 10");
return;
}
try {
String ip_adrs = argv[0];
int unit = Integer.parseInt(argv[1]);
int reg_no = Integer.parseInt(argv[2]);
int num_regs = Integer.parseInt(argv[3]);
System.out.println(
"ip_adrs = "
+ ip_adrs
+ " unit = "
+ unit
+ " reg_no = "
+ reg_no
+ " num_regs = "
+ num_regs);
// set up socket
Socket es = new Socket(ip_adrs, 502);
OutputStream os = es.getOutputStream();
FilterInputStream is = new BufferedInputStream(es.getInputStream());
byte obuf[] = new byte[261];
byte ibuf[] = new byte[261];
int c = 0;
int i;
// build request of form 0 0 0 0 0 6 ui 3 rr rr nn nn
for (i = 0; i < 5; i++) obuf[i] = 0;
obuf[5] = 6;
obuf[6] = (byte) unit;
obuf[7] = 3;
obuf[8] = (byte) (reg_no >> 8);
obuf[9] = (byte) (reg_no & 0xff);
obuf[10] = (byte) (num_regs >> 8);
obuf[11] = (byte) (num_regs & 0xff);
// send request
os.write(obuf, 0, 12);
// read response
i = is.read(ibuf, 0, 261);
if (i < 9) {
if (i == 0) {
System.out.println("unexpected close of connection at remote end");
} else {
System.out.println("response was too short - " + i + " chars");
}
} else if (0 != (ibuf[7] & 0x80)) {
System.out.println("MODBUS exception response - type " + ibuf[8]);
} else if (i != (9 + 2 * num_regs)) {
System.out.println("incorrect response size is " + i + " expected" + (9 + 2 * num_regs));
} else {
for (i = 0; i < num_regs; i++) {
int w = (ibuf[9 + i + i] << 8) + (ibuf[10 + i + i] & 0x00FF);
System.out.println("word " + i + " = " + w);
}
}
// close down
es.close();
} catch (Exception e) {
System.out.println("exception :" + e);
}
}
