The modular nature of the Tower system is due to the fact that every I/O line from the main processor is passed up through the entire stack to every layer connected. Two 18-pin headers provide connections for all 33 standard I/O pins on the PIC Foundation and 13 I/O pins on the Rabbit Foundation, as well as primary and secondary power busses and an electrical ground connection.

Connector pinout is shown in the diagram below:



Each layer uses four 18-pin surface-mount connectors, with two female headers on the top of the board, and two male headers on the bottom.

Tower layers all have their own, independent PIC microcontroller. Communication between the main processor and the layer microcontrollers is accomplished via the industry-standard I2C serial protocol. This 2-wire protocol contains clock and data lines, which are located on breakout pins RC3 and RC4 respectively.

Power can be drawn off of either a primary or secondary power bus, each of which can be powered separately by the foundation layers. Modules that anticipate higher power drain, such as the Servo Motor module, are designed with switches to allow the user to switch which bus they are powered off of.