Hardware and Software Design • Manufacturing Services
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flag; when the output FIFO is not Empty data is moved into the holding register. The Valid bit is set when data is
ready to be read and cleared when the data is “stale” or not updated.
READ_EN_DMA when ‘1’ enables the read state-machine in the DMA mode. When the PLX device accesses from
the DMA read address; the state-machine starts up, and when the Output FIFO of Channel has at least 1/2 FIFO of
data will respond to the access by asserting READYn. Data is continuously supplied to the PLX device until
BLASTn is asserted. [1 data word per PCI clock to support a burst transfer]. When the burst is completed and
BLASTn is asserted the pipeline stops and holds the current data. When additional reads from the DMA read
address take place the process restarts with the data in the pipeline. Due to PCI requirements, the burst length is
limited to approximately 250 clocks per burst. The FIFO debth is 1K. Starting with 1/2 FIFO guarantees that the
FIFO will not run dry during a burst transfer. Channel 0 and 4 are used to Retrieve data. When channel 0 or 4
reaches the “Done” condition so that all requested data is stored into the FIFO the 1/2 full requirement is “waived”
to allow the DMA counter in the PLX device to complete the transfer and not get stuck needing less than 1/2 FIFO
of data to complete. The length counter in the Address Generator must be coordinated with the PLX DMA count
requested. See the Address Generator and Operational section for more information.
Only one of the two reads should be selected at a time. To change modes, select neither then select the channel
then select the mode.
Channel when ‘0’ select Output FIFO 0 which corresponds to channels 0-3. When ‘1’ selects Output FIFO 1
corresponding to channels 4-7. Channel should be selected before selecting Read Std or Read DMA. Unexpected
results will occur otherwise. Turn off read standard and read DMA. Select channel. Reset FIFO if needed. Enable
read mode.
LED Control when ‘1’ will turn on the LED and when ‘0’ will turn off the LED. Rev 02 boards and later.