This board is essentially a digital I/O driver. The FPGA signals drive signal conditioning hardware (consult your custom system integration documentation for the list of boards included with your simulator), other communication hardware and all dedicated hardware using SPI or other interfaces.
The center FPGA is the main component of the OP7000. The board manages the 256 I/O channels, however, its mid-plane connector can handle only half of these lines. A piggy-back module, the FPGA mezzanine (P/N 126-0326) is used to route the other half of the I/O lines to a second mid-plane connector.
However, if additional FPGA boards (secondary) are used in the OP7000, these additional boards do not require the FPGA mezzanine.
OP7161 FPGA board, top view:
FPGA mezzanine board: