Copyright © 2015 Robot Circuits, LLC
10
RCAT-1A Rev A3 Designer’s manual
Serious Power for the Serious Designer
Major Subsystems
The RCAT™ control board comprises several major subsystems. Some of these subsystems are broken out to connectors
on the board for access by external user hardware. Others are not. Still others have access to the outside world through
interim circuitry. For example, the extended RAM subsystem is not broken out for external access. This means that CPU
ports PA0 through PA7, PC0 through PC7, PG0 through PG2 and finally PJ7 are dedicated to this subsystem and thus are
not brought out to external connection points. Consider the extended RAM subsystem schematic:
Figure 4
We call such subsystems “
dedicated
” in that they use CPU ports fully dedicated to nothing other than the subsystem.
As mentioned above, other subsystems have breakout points on various connectors. These may be “
direct
” connections
to the CPU or they may be “
indirect
” connections. An example of an “indirect” subsystem is the USB interface subsystem
shown here:
Figure 5
As you can see, CPU ports RXD0(PE0) and TXD0(PE1) connect to the USB bridge chip and then to the external world
through the bridge. Although you have “access” to the ports, it is “indirect” through an onboard device (the CP2102 USB
chip).
The “direct” access subsystem consists of 37 connections broken out on J5 as shown here:
