SDI
Tektronix 11000-series scopes use a serial digital protocol for communication between the mainframe and the plug-ins. This communication mechanism is called Serial Digital Interface (SDI). SDI was designed by Lester Larson.
SDI is bidirectional: The mainframe can send messages to the plug-ins; the plug-ins can send messages to the mainframe. SDI uses three signals:
- SDI Clock
- SDI Mainframe to plug-in data
- SDI Plug-in to mainframe data
The signals are 5 V TTL. The clock is a 4 MHz square wave running all the time.
In the 11301 mainframe, SDI communication is controlled by the U1760 SDI IC (Tektronix part number 156-2622-00), which is on the A11 Main Processor board, at the top rear of the scope.