Transmission control device, memory control device, and PLC including the transmission control device

A transmission control device comprising:

• a data storage memory in which data are written;
• a plurality of data copy memories into which the data written in the data storage memory are copied;
• an unread copy-memory selection unit that selects a first data copy memory from which the data is not read out, from among the data copy memories;
• a memory copy unit that copies data written in the data storage memory into the first data copy memory selected by the unread copy-memory selection unit;
• a read copy-memory selection unit that is on standby until the memory copy unit has completed copying data, and selects the first data copy memory into which the data has been copied when the memory copy unit has completed copying the data;
• and
• a data output unit that reads data from the first data copy memory selected by the read copy-memory selection unit and outputs the read data to a transmission unit.