GBS Elektronik MCA-527 Oscilloscope Mode - Manual (Page 6)

MCA527
2.4 Transferring Oscilloscope Data
The oscilloscope data are transferred with the firmware command CMD_QUERY_OSCI_SCREEN. This
command is only callable during a running oscilloscope measurement. The use of the firmware command
depends on trigger source and resolution.
2.4.1 Triggered Measurement, Resolution = 100ns
In this case, the parameter of the firmware command CMD_QUERY_OSCI_SCREEN is ignored. The value
at byte offset 0 of the result data array is the start position of the received data within the MCA527 data
memory. With the assistance of this value, the application can check the validity of the received data (byte
offset 8). If it is unequal -1, the data are valid. If it is equal to the value returned by the previous call of the
firmware command, the data are unchanged. The received data corresponds to the ADC value of 500 data
points.
2.4.2 Triggered Measurement, Resolution > 100ns
If the interval between two data points is greater than 100ns, several samples are condensed corresponding
to the resolution to one data point. Each data point consists of a data pair, minimum and maximum value of
the condensed samples. As a consequence of this, the firmware command CMD_QUERY_OSCI_SCREEN
must be called twice for transferring 500 data points. At the first call of the firmware command, the
parameter must be -1. The application has to check the start position of the received data (byte offset 0 of
the result data array). If it is unequal -1, the received data (byte offset 8) are valid and the application has to
call the firmware command a second time to transfer the second data half. This time the parameter must be
equal to the start position of the subsequent data (byte offset 4 of the result data array of the first firmware
command call). The application has to check the start position of the received data (byte offset 0 of the
result data array) again. There are three possible results:
1. The value (start position of the received data) is equal to the passed parameter (start position of the
subsequent data). In this case, all 500 data points has been successfully received.
2. The value is equal to -1. In this case, the subsequent data are no more available. The application must
restart the transfer with the first firmware command call.
3. The value (start position of the received data) is unequal to the passed parameter (start position of the
subsequent data). In this case, the received data are not the subsequent data, because they are no
more available, but new data are available. The application can take this data as the first data half and
has to transfer the second data half by a further firmware command call with parameter equal to the
start position of the new subsequent data (byte offset 4 of the result data array of the previous
firmware command call).
2.4.3 Untriggered Measurement
The firmware command CMD_QUERY_OSCI_SCREEN is called with parameter equal to -1. If the
resolution= 100ns, the received data are ready to use. If the resolution > 100ns, the firmware command has
to be called a second time to transfer the second data half. This procedure is similar to procedure described
in section 2.4.2.
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