The boards have a built-in 4-digit 7-segment LED display and it requires a minimum of only one I/O line to control it. It is possible to control the display through two different communication interfaces: Serial TTL or I2C.
In addition to standard hexadecimal characters, other special characters can be visualized; it is also available an independent control of decimal points, apostrophe and colon.
Communication protocol is very simple and all the informations are sent in a single byte. The most significant two bits represent the character set to be used, further two bits indicate wich one of the 4 digits is having a change and the last significant 4 bits specify the character to visualize.