How to send such complicated hex, binary protocol data accurately using java byte[]?

Question

I am very confused with this kind of stuffs, What should I send as final command, get always confused 8 bits to 1 byte but how do we make it? Is it only the command packet [

Answer 1

• In such diagram header block shows mostly like "Bit 7, Bit 6,..,Bit 0" instead of "Bit 0, Bit 1, Bit 2, ... Bit 7", i always wondering why?.

In typical number writing 0 is the least significant bit 7 the most significant and the byte is written in most significant to least significant 7-0.

byte  11111111
place 76543210

• But when i apply in code what is following order for byte st[0] = Bit 7 or Bit 1?

In your code this is not setting bits this is setting a byte in the byte array

If you are nervous about setting bits try a class like this:

public class SimpleByteSetter {

  /* b is is byte you are setting
     on is if the bit is set to on or 1
     place is the bit place in the range of 0-7
  */
  public static byte set(final byte b, final boolean on, final int place) {
    if (on) { return (byte) (b | ((1 << place) & 0xFF)); }
    return (byte) (b & (~((1 << place) & 0xFF)));
  }

  // 1 == on everything else off (but only use 0!)
  public static byte set(final byte b, final int on, final int place) {
    return set(b, 1==on, place);
  }

}

use it in you code like:

byte header = 0;
// get = 0, set = 1, place = 0
header = SimpleByteSetter(header, 0, 0 ); // get
// header 2 byte = 0, header 2 byte = 1, place = 1
header = SimpleByteSetter(header, 0, 1 ); // header 1 byte
...
st[0] = header;

• Also according to this diagram, does it mean every command i send will have Header fixed always

Yes

• This is the code i was trying by taking Bit 1 as st[0], Bit 2 as st1 instead of Bit 7 as st[0]. To apply Power off/on test.

I don't have enough information to actually build the packet but:

// the header is 1 byte I don't see how to make it two
// the command is 2 bytes per the table
// the parameter length is 0 so 1 byte (is there suppose to be a device id?)
byte[] st = new byte[ 1 + 2 + 1 ];

byte header = 0;
// get = 0, set = 1, place = 0
header = SimpleByteSetter(header, 0, 0 ); // get
// header 2 byte = 0, header 2 byte = 1, place = 1
header = SimpleByteSetter(header, 0, 1 ); // header 1 byte
// length 1 byte = 0, length 2 byte = 1
header = SimpleByteSetter(header, 0, 2 );
// command 1 byte = 0, command 2 byte = 1; 
header = SimpleByteSetter(header, 1, 3 );

st[0] = header;
st[1] = 0x0130 & 0xFF; // poweroff command first byte
st[2] = 0x0100 & 0xFF; // poweroff second byte
st[3] = 0;