System Circuit Diagram - FIGnition FUZE Hardware Reference Manual

8. Arduino Headers.
The block diagram tells you some basic information about the structure of the computer.
For example, the arrow between USB and CPU is two-headed, because data goes in both
directions. The arrow from the keypad is single-headed, because data only goes from the
keypad. RAM and Flash share a multi-head arrow, because data transfer is shared be-
tween them.

1.1 System Circuit Diagram

A circuit diagram for FIGnition represents a detailed, logical diagram of the computer, a
schematic; showing all components and their connections to every signal. Every section of
the FIGnition hardware reference starts with its part of the circuit diagram.
As you can see, components on the circuit schematic don't look like real-life. In addition
some of them aren't in the same places as on the PCB (e.g. USB isn't really in the middle
of the PCB) and this is done to make the logical relationships clearer. Finally, the keypad
looks like it's disconnected, but it's not really, instead each disconnected wire is labelled
and wherever else you see the same label the wire continues from there. For example,
/SWROW1 on the keypad also appears on the right-hand edge of the U1 rectangle, next to
the number 13 . This means the /SWROW1 connection on the keypad connects to pin 13 of
U1 (the CPU).