Agilent Technologies VXI E1439 - Manual (Page 60)

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Using the Agilent E1439
Fiber Optic Interface
Append
The Append fiber mode copies optical data from its fiber receiver to its fiber transmitter and
appends its own filtered ADC data. This mode is required in an optical fiber append chain. For
the first module in an append chain, set the fiber mode to Generate, BOF to ON, and Epoch
Generate to ON. The module generates data epochs in the standard fashion and a BOF is sent after
each epoch. For all modules after the first, set fiber mode to Append, BOF to ON, and Epoch
Generate to ON. Each module copies received data to its transmitter output until a BOF is
received. The module then sends one epoch of filtered data from its ADC (if at least one block is
available), followed by a BOF.
In block data mode, the data from a single trigger is transmitted. Subsequent triggers should not
be generated faster than the data can be transmitted.
In continuous data mode, the generated data must not exceed the available fiber bandwidth,
allowing the data to be merged without data loss from a FIFO overrun. Therefore, you must
reduce the generated sample rate using either an external sample clock operating at a slower rate
or data decimation. If you use an external sample clock operating at a slower rate, epoch size must
be 1024 bytes (a larger epoch size causes a FIFO overrun resulting in a loss of data, and a smaller
epoch size increases overhead reducing the available bandwidth). The available bandwidth is then
about 101 MBytes/second or 238 MBytes/second. If you use data decimation, an epoch size of
approximately 2048 bytes provides the maximum available bandwidth.
Note
Epoch size and block size must be equal (in bytes). Since block size is in samples, you can
multiply block size by the number of bytes per sample to determine the equivalent epoch size.
Conversely, you can divide the epoch size by the number of bytes per sample to determine the
equivalent block size. Real 12-bit data contains 2 bytes per sample, complex 12-bit data and real
24-bit data contains 4 bytes per sample, and complex 24-bit data contains 8 bytes per sample.