CAS Overview
General page including external interfacing documentation.
Last updated
General page including external interfacing documentation.
Last updated
The Common Avionics System (CAS) is a system for Avionics hardware development with the primary motives being to reduce hardware development time by better leveraging existing verified designs. CAS achieves this by splitting functionality into separate modules. This allows each module to do one thing and do it well, without having to redo aspects of the system that have already been done. CAS will allow Avionics to more easily support new projects and will reduce risk (in the long-term) by reusing well-tested designs.
CAS Board standards document (describes how to develop modules for CAS):
Stack: A set of modules placed vertically with standoffs separating them.
Module: A single printed circuit board (.062" thickness) that has the hardware to satisfy a certain function.
See image below for cross-section of a stack (specifically of a module). The modules are square PCBs with 4 mounting holes in the corners (large filled yellow circles with blue-green halo). The arrays of smaller empty yellow holes are header pins for connection to other modules in the stack.
The side to side distances are 2.5 inches and mounting hole to mounting hole distances are 2.2 inches. The space from the top of a module to the bottom of another module is 0.6 inches.
The types of pins that appear on the bus are:
Power
+3.3V
+5V
+BATTERY
GND
I2C0
SCL
SDA
I2C1
SCL
SDA
SPI High-Speed
SCK
MISO
MOSI
SS1, SS2
SPI0
SCK
MISO
MOSI
SS1, SS2, SS3, SS4, SS5, SS6, SS7, SS8
Interrupt pins
INT1, INT2, INT3, INT4, INT5, INT6, INT7, INT8
The entire CAS stack's voltage rails (3.3V and 5V) are powered by a power management unit located on the core board. This power unit on the core board recieves +7.3V DC from an external battery. The entire CAS stack generally draws below 50 mA of current when not doing power-intensive tasks.
To separate modules from each other, use a flat-head screwdriver as a lever, as shown in this picture:
All of the modules in CAS share a common 80-pin bus. Not all of the pins have functions assigned yet, but they may be assigned in future modules. The CAS modules must never conflict with the common bus pin-to-function assignments. The pin-to-function mapping is recorded in this google sheet:
