2.3.6.2 Interfaces

All ten subsystems within the DEA are identical and independent. They are each interfaced to other ACIS components in the same way. Each subsystem interfaces with the CCD it services via three groups of signals for each CCD: the clocks and the biases, which are driven from the subsystem to the CCD, and the video signals coming from the CCD to the subsystem for processing.

Each subsystem of the DEA interfaces with the DPA via four ports, two to the FEP and two to the BEP. The BEP ports allow the DEA subsystems to receive commands and to send status and housekeeping data. Both ports are identical to ensure fault tolerance and redundancy capabilities. The BEP can talk to the DEA subsystems individually or go into broadcast mode and talk to all ten subsystems simultaneously. The FEP ports allow the DEA to send digitized video data to the FEP from all CCDs simultaneously. Each FEP port can be assigned to any CCD, but at any one time it must be dedicated to a single CCD and can receive pixel data at a maximum throughput rate of 400 kilo-pixels per second.

Each DEA subsystem has a port which allows ground support equipment (GSE) to monitor the CCD video data streams, acting exactly like the FEP ports discussed above. Each port listens to the CCD that the DEA subsystem services.