The ESI module consists of 5 major functional elements:

The ESI module has implemented 3 logical communication ports. Port 1 and Port 2 are used to communicate to external serial devices while Port 0 is used for programming the module. Port 0 and Port 1 share one physical port. All 3 ports can be set up independently. For a detailed description of the port setup see Port Command.

The ESI module exchanges data with the Quantum controller through the use of 12 output words for commands and data from the Quantum controller and 12 input words for data to the Quantum controller and command echo and status information. For detailed information about the structure of the command and response structures see ESI Command Word.

The 2 physical ports of the ESI module have an input and an output buffer of 255 characters each. The device side of those buffers is maintained automatically by the optional XON/XOFF handshake. For data transfer from and to the Quantum controller, for buffer control and status testing several commands are available which are described in detail in Data Flow.

The ESI module has a 32 kbyte memory which is organized as 16k 16-bit registers. These registers hold all data coming from and going to the serial ports. They can be accessed by the PUT and the GET command.

The ESI module can hold up to 255 ASCII messages with 127 characters plus checksum character each. These ASCII messages can be either static texts to be sent to an external device or a definition of how data contained in the register area is to be translated into or from a stream of serial ASCII characters, or a combination of both.

The firmware of the ESI module can be loaded over the local I/O backplane. Upgrades and changes in functionality are supported by updating the flash executive firmware within the ESI module. Users should be aware that the update procedure can only occur over the local I/O backplane, even though the module can be placed in local, remote, or distributed locations. If you are using the ESI module in remote or distributed backplanes, plan on having an empty slot available in the local backplane, or a spare controller system to accommodate future executive upgrades.