1. Command and Data Handling
Winkelman, Martin
Jayaraman, Vijay
Bhatia, Vishal

2. Introduction
Command and Data Handling subsystem is responsible for computing and control of subsystem functions.
The core of this subsystem is a single- board computer powered by the Intel PXA255 Processor with the PC/104 form factor.

3. System Functional Diagram
FLIGHT COMPUTER
General Purpose I/O Pins
SERIAL PORTS
+5v
PC/104
USB
POWER
ADCS
SCIENCE
TIP-MASS
MECHANISMS
RS232 Serial
I/O Board
CPLD
Serial to b bridge
802.11b
TNC
RADIO
COMM
THERMAL
INTERFACE
THERMAL
INTERFACE
THERMAL
INTERFACE
THERMAL

4. Design Changes Since PDR
Externally triggered reset is no longer design requirement
External watchdog provided by power system
We will try to avoid multiplexing inputs if possible
Additional 32MB flash memory needed
Interface requirements have changed for some systems
Serial link to b bridge now used for tip mass in place of using b card on computer
Science will also be using a serial port
Some systems have added analog and/or digital interface lines

5. Functional Requirements
C&DH must not exceed 7 Watts.
Maximum ½ kg.
External watchdog timer.
3.8” x 3.6” x 4” profile
Must run Linux
32MB RAM minimum
16MB FLASH + additional 32 MB FLASH

6. Interface Requirements
System Digital Out Digital In Analog Out Analog In Other I/O
ADCS
Comm x serial
Power serial
Mech
Science serial + 2x USB
Thermal
Tip Mass serial
TOTALS serial, 2 USB

7. Design Compliance
All digital I/O, serial, and USB ports are built in to Viper
Additional flash memory will be installed in the CompactFlash socket
Analog I/O will be provided by additional COTS board using PC/104 bus

8. Safety Requirements System is contained within a closed box
System ground will be isolated from structure ground
System is not active without power
There are no high current inputs or outputs
There are no moving parts

9. Arcom Viper PXA255 400Mhz CPU SDRAM: 64M FLASH: 16M
256K Battery Backed SRAM
Real-Time Clock
Watchdog Timer
Interfaces:
2 USB v1.1
5 Serial Ports
Compact Flash Drive Support
Ethernet: 10/100BaseT
JTAG
8 Digital In / 8 Digital Out
PC/104

10. Specifications – Viper Overview
Power Requirements:
+ 5V only supply (typical)
+5V (standby mode)
Operating Temperature:
-20°C to +70°C
Weight:
96 Grams
Form Factor: PC/104

11. PC/104 Module Form Factor

12. Design Details
Current design anticipates using 3 industry standard PC/104 size boards.
Analog Inputs/Outputs will be provided by a PC/104 expansion board.
Custom circuitry, if necessary, will be simple, such as a multiplexor or thermistor driver.

13. Analysis and Prototyping
Some software testing has already been done on Computer
No prototyping necessary for COTS components as long as interface specifications are followed

14. COTS Parts Status Different options are still being evaluated TBD
I/O boards
1 has been procured
Arcom Viper
Status
Availability
Part
Lead time of less than 2 weeks

15. I/O Board Make or Buy Rationale
Better selection of interface options
High reliability components can be selected
Buy
Can fit more interfaces on a board
Software implementation is much simpler
Not much more expensive than fabricating custom board
Conclusion: We will buy the I/O board

16. Manufacturing and Testing Constraints
Boards connected using PC/104 mountings
Wiring will be soldered to connectors
Testing
Most testing will be done with software simulation and readily available test equipment
JTAG can be used to troubleshoot system hangs

17. Ground Support Equipment Requirements
Power system must be integrated before C&DH integration
A standard 5 volt power supply can be used when testing system before power is integrated
Ethernet Port on Viper will be used for testing during integration
The serial port can also be used for testing until the Comunications system is integrated

18. Documentation Design Review Test Plan Trade Studies
Preliminary Design Review
Peer Review
Test Plan
Outline for C&DH system
Trade Studies
Arcom Viper vs. other PC/104 computers
To read over any of the following topics please go to

19. C&DH Schedule Interface Board Custom Hardware End of Semester Review
March Select and procure I/O board
April 5-9 Testing
Custom Hardware
March Determine if custom board is needed
March 29 – April 2 Design and testing
April Testing
End of Semester Review
April Integrate all boards together
April 25 – May 10 Testing

20. Issues and Concerns Unknown effects of radiation on COTS parts
Final choice for I/O board has not been made