6 Slot Backplane

A backplane which supports up to six expansion cards, meant to go into a 3U VME crate.

Features

• Direction-controlled buffers for address and data bus
• Mixer for audio from CPU board and expansion slots
• Detection of installed peripheral cards via detect lines
• An I²C bus switch to allow CPU board independent access to each slot’s sideband bus
• Extremely low jitter clock distribution

It’s intended to be used in conjunction with the backplane management card for power, but the required +5V and +12V rails can also be provided through a 3.81mm pitch pluggable terminal block instead.

Assembly Notes

Here are some notes about hardware revisions.

Rev 1

• The ID EEPROM is an AT24CS16, which has a different protocol than the AT24CS32 specified in the schematic. The address pins are also "NC" there
• Drop resistors for orange/yellow LEDs (R401, R107, R108) should be a lower value
  • R401 probably got assembled wrong
• Drop resistors for yellow LEDs (R101, R102) should be slightly higher
  • Or, we just spec shittier green LEDs
  • They're just slightly too bright