Communication device and communication system

A communication system, comprising:

• a Master SerDes including a first LINK;
• and
• a Slave SerDes including a second LINK, wherein
• the first LINK generates a first output signal on a basis of a first external signal from a Master, outputs the first output signal to the Slave SerDes, generates a third output signal on a basis of a second output signal from the Slave SerDes, and outputs the third output signal to the Master,
• the second LINK generates the second output signal on a basis of a second external signal from a Slave, outputs the second output signal to the Master SerDes, generates a fourth output signal on a basis of the first output signal from the Master SerDes, and outputs the fourth output signal to the Slave, and
• each of the first output signal, the second output signal, the first external signal, and the second external signal includes
• command information indicating content of a command transmitted from the Master,
• final-destination-device-identification-information for identifying the Slave,
• internal address information indicating an internal address of the Slave,
• data length information indicating a length of data transmitted from the Master, and
• data-end-position-information indicating an end position of the data transmitted from the Master.