Communication unit and communication system

A communication system comprising:

• a first communication unit;
• and
• a second communication unit that transmits transmission data to the first communication unit,
• one or both of the first communication unit and the second communication unit including
• a communication circuit section that receives transmission data divided into head data and one or more subsequent data from an communicated unit over a period of a plurality of time-segments,
• a storage section having a storage region in which at least the transmission data received by the communication circuit section is stored, and
• a control section that places a limitation on an access period to cause a period of access to the storage region in a period of a time-segment in which the subsequent data is transmitted to become shorter than a period of access to the storage region in a period of a time-segment in which the head data is transmitted.