DTE20 Ten-Eleven Interface
The DTE20 Ten-Eleven Interface (also called the DTE20 Console Processor Interface) is a peripheral on KL10 CPUs which allows a PDP-11 to act as a front end. Depending on how the DTE20 is configured ('restricted' or 'privileged'), it can be just for off-loading I/O functionality to the PDP-11 (both to reduce the load on the main CPU, but also to allow access to the wide range of peripherals supported on the PDP-11), or it can also function as a control and diagnostic system for the main CPU: loading microcode, bootstrapping, etc.
A KL10 may have up to 4 DTE20's, and a PDP-11 may host up to 4 DTE20's on different kL10's.
The DTE20 is connected to the EBox of the KL10 via the EBus; privileged DTE20's also have access to the KL10's diagnostic bus. To the PDP-11, it appears as a normal UNIBUS peripheral.
A 'restricted' DTE20 consists of a pair of hex boards (M8552, M85553) and a dual card (M8554), plugged into an I/O backplane of the KL10 (along with the RH20s). These are connected to a UNIBUS connector mounted lower down in that rack, and a BC11A cable from the PDP-11 (usually a PDP-11/40) plugs into that.