Backplane

The SNObus crate is largely a mechanical support for the SNObus backplane. The backplane is intended to provide all interconnections needed between FECs, Translator, and Trigger cards, to distribute power to these boards and to maintain a high quality transmission line environment with a low level of radiated EMI. To this end we have adopted a number of slightly unusual features - most of which should be transparent to systems outside the SNObus crate.

• All signals on the backplane are low level -
  • Data, Address, and Control lines are 0.8V swing GTL
  • Clocks are differential ECL (0.8V swing also)
  • DTACK and Data Available are single ended ECL
• All signals are terminated (properly, we hope)
• The number of GND pins is greatly increased relative to VME

In addition, because the Trigger card needs J1, J2, and J3 connectors and the Translator needs J2 and J3 but the FECs only use J2 it is necessary to make a rather unusually shaped backplane - somewhat like a scorpion as shown in Figure 6.

• Main Busses
• Point to Point Control Signals
• Geographic Information
• Trigger
• High Voltage