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Flush Data FIFO Command
The data FIFO should be flushed before data acquisition is initiated by the trigger/arm
command, but not until after the scan list has been configured. The flush command may also
be followed by FIFO threshold programming. After the FIFO is flushed, the FIFO empty flag
will be set to “1” and the almost full and full flags reset to “0”. Anytime the data FIFO is
flushed, the default threshold setting will be restored (7 bytes to full) by the hardware. The
data FIFO threshold should always be programmed after flushing if the required threshold is
different from the default one.
5.2.6.4 A/D Stop Command
Once data acquisition is initiated by the trigger/arm command, it can only be stopped by
receiving the A/D stop command. The A/D stop command should be issued as soon as the
required data points are collected to prevent data FIFO overflow. Data FIFO overflow is the
only flag that indicates lost data during the acquisition process. Without the stop command,
the A/D can continue to run, filling the data FIFO. When the FIFO is full, it will ignore data
samples coming from the A/D converter.
5.2.6.5 Data FIFO Program/Access Control
The A/D data FIFO has two programmable thresholds, almost empty and almost full, and two
associated flags. The almost empty threshold and flag are not used. By default, the thresholds
are set to 7 bytes (7 to full and 7 to empty) when reset, powered up or anytime the FIFO is
flushed. It can be programmed to any value between 1 and FIFO size - 1 (in bytes).
To program the FIFO threshold, make sure the A/D has been stopped. Set this bit to “0” by
writing an all “0” byte to the auxiliary control register. Then send an A/D FIFO flush
command with the same bit setting by writing a byte of 40H (hex 40) to the same register.
This will put the FIFO into program mode. The following read/write operation will be
directed to the threshold registers instead when accessing the data FIFO at base +1. The 4 byte
threshold setting should be written into the data FIFO by doing four consecutive write
operations. Optionally, the threshold setting can be read back for verification by doing four
consecutive read operations. Table 5-17 lists the 4 byte threshold setting format.
Table 5-17. Data FIFO Threshold Setting
0..15 (2K option)
High byte of the almost full threshold
3
0..255Low byte of the almost full threshold2
0..15
High byte of the almost empty threshold
1
0..255
Low byte of the almost empty threshold
0
Valid RangeDefinitionByte
DAQP-208/208H/308 Users Manual 52