// Encode "TEST" (0x54 0x45 0x53 0x54)
        // T=0x54: upper nibble 0x5->F(0x46), lower nibble 0x4->E(0x45)
        src[1] = 'F';
        src[2] = 'E'; // T
        // E=0x45: upper nibble 0x4->E(0x45), lower nibble 0x5->F(0x46)
        src[3] = 'E';
        src[4] = 'F'; // E
        // S=0x53: upper nibble 0x5->F(0x46), lower nibble 0x3->D(0x44)
        src[5] = 'F';
        src[6] = 'D'; // S