2022-7-13 Backplane Meeting

Date

13 Jul 2022

Topic	Notes
Communication Interface (CAN, Ethernet, other options)
Narrow down requirements Backplane Architecture Requirements

Metric	Ethernet better	CAN better	Impact and why
Cost		X	Low - Difference is that of Ethernet chips, switches, and supporting passives
Software complexity	X		High - less software bandwidth; more experience with Ethernet implementation
Hardware complexity		X	Medium - More careful routing required, more traces in general, but that is concentrated to the backplane and we have hardware engineering bandwidth
Data Bandwidth	X		Medium - CAN precludes video over the bus
Physical size		X	Low - Not that much worse
Module testing	X		High - Individual modules easier and there are many of them
Backplane testing		X	Medium - Fewer points of failure to troubleshoot but is very important
MCU compatibility	X		Low - Lots for either
Power		X	Medium - Ethernet very slightly violates modularity philosophy due to having ICs on the backplane + Ethernet switches require more current

Summary:

Additional notes:

Ethernet violates modularity because there are ICs on the backplane that need to be tested, requiring the power board, which isn't the case for CAN because the CAN bus doesn't have ICs
Wiznet chips (130 mA active, 13 inactive) and switches draw a significant amount of current, but power considerations can be mitigated by better design or operations planning
- Power might push us in favor of a more expensive 8-port switcher
- Can also limit the number of modules
Stock considerations are not relevant because the bottleneck is the microcontroller in either case.

Decision: Ethernet, due to high impact tradeoffs.