如何组合三个连续的Modbus寄存器以得到一个整数值？

Question

我必须使用Modbus协议读取设备的值。它有一个6字节长的值，由三个连续的保持寄存器表示。这是有符号类型和无符号类型的图形表示。

我可以使用Java中的Modbus库读取三个寄存器。每个寄存器作为一个2字节的短值读取。现在我需要知道如何组合这三个值来形成一个有符号和无符号格式的整数值？

Answer 1

请记住，我已经很久没有写java了，所以我的java已经生疏了。因为Java中没有无符号值，所以这有点难。尝试如下所示：

class ModbusConvert
{
    public static long toUnsigned(int register0, int register1, int register2)
    {
        //NOTE: Assumes long is 64-bit, int is 32-bit

        // Convert each register to a long in the appropriate bit position and OR them together
        long v2 = (((long)register2) & 0x0FFFF);
        long v1 = (((long)register1) & 0x0FFFF) << 16;
        long v0 = (((long)register0) & 0x0FFFF) << 32;
        return v0 | v1 | v2;
    }

    public static long toSigned(int register0, int register1, int register2)
    {
        //NOTE: Assumes long is 64-bit, int is 32-bit

        // Convert each register to a long in the appropriate bit position and OR them together
        if ((register0 & 0x8000) != 0) register0 |= 0xFFFF0000; // Sign extend

        long v2 = (((long)register2) & 0x0FFFF);
        long v1 = (((long)register1) & 0x0FFFF) << 16;
        long v0 = ((long)register0) << 32;
        return v0 | v1 | v2;
    }

    public static void main(String args[])
    {
        // Example Register Values (value = 0xFEDC76543210)
        int register0 = 0xFEDC;
        int register1 = 0x7654;
        int register2 = 0x3210;

        long unsigned = toUnsigned(register0, register1, register2);
        long signed = toSigned(register0, register1, register2);

        System.out.println(String.format("UNSIGNED: 0x%016X", unsigned));
        System.out.println(String.format("SIGNED  : 0x%016X", signed));
    }
}

The output is:
UNSIGNED: 0x0000FEDC76543210
SIGNED  : 0xFFFFFEDC76543210