Agilent Technologies 16900A, Руководство по обслуживанию

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112 16900A, 16902A, and 16903A Service Guide
8
Theory of Operation
temperature range. The purpose of this circuit is to increase
air flow as needed while maintaining the lowest possible fan
noise.
16900A/16902A Input/Output Board
Top level function
The input/output (I/O) board bridges between the frame rear
panel connectors and the MIB (module interface board) from
which it receives power and system interface signals.
The board has three basic purposes:
1
Interface hardware for the following system frame
connectors:
• multiframe input/output
• target control port
• trigger in/out
• clock in
• calibration out.
2 System clock generation and synchronization.
3 System level functions for the module slots. Specifically:
• correlation
• trig/arm/flag routing
FPGA function
The Xilinx XC2V250 FPGA is the heart of the I/O board and
contains almost all of the functional logic for this module.
The system interfaces directly to this part in the same way
it talks to the six module slots, via a 16 bit multiplexed
general purpose bus. The FPGA is loaded from an on board
EPROM at power up. The EPROM contents can be changed
(updated) through the system software via a JTAG port.
A major function of this FPGA component is system
correlation; time alignment of the six modules and possible
other modules connected through the multiframe port or
trigger- in connector. This is done with eight 52- bit counters
running at 1.6 GHz allowing relative time alignment of eight
seperate events. A 100 MHz clock is also selected from
three possible sources (internal, multiframe, external) and a
synchronizing signal is generated for time alignment across
multiframe.