A/D converter and programmable controller system

An analog/digital (A/D) converter that is attached to a programmable controller (PLC) and sequentially converts an analog value inputted from outside into a digital value, the A/D converter comprising:

• a shared memory that is read-accessed from a CPU unit that controls the entire PLC and includes a log storage area with a ring buffer configuration for sequentially logging the digital value and a parameter storage area for storing a head pointer serving as a parameter indicating a position where a next log data is stored;
• and
• a logging executing unit that writes a digital value in an address indicated by the head pointer in the log storage area as log data, updates the head pointer, and after stopping logging, changes storage positions of respective log data stored in the log storage area based on the head pointer to arrange the positions in a time series.