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.