The following diagram follows the entire path of the Scanning Interface Unit (SIU) v2.2 video B/C/D input circuits.

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Notes:

• Scanning Interface Rev 2.2 is printed on the card inside the SIU.
• SEII Rear Panel Connector is that of the computer card.
• Scanning I/O A is an SIU rear panel connector.
• The circuit shown is inside the SIU.
• The video signal from the microscope enters the SIU at pin 4/5/6 of Scanning I/O A.
• The op-amp circuits add gain and offset.
• The video enters the SEII computer card at pins 9/10/11.
• Scanning I/O A is unable to output the video for switching needs the way Scanning I/O B is.
• The relay switches both the signal and ground.