The following diagram follows the path of the Scanning Interface Unit (SIU) v1.1 relay enable circuit.

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Notes:

• Scanning Interface Rev 1.1 is printed on the card inside the SIU.
• SEII Rear Panel Connector is that of the computer card.
• Scanning I/O B is an SIU rear panel connector.
• The circuit shown is inside the SIU.
• The SEII generates single logic signal which drives Q1.
• Q1 drives relay RL3.
• RL3 provides the external enable signal to the microscope via Scanning I/O B pin 2.
• RL3 also provides the a 12V signal (RELAY_EN) to the rest of the relays on the SIU board.
  Schematics for these relays can be found with their respective circuits.