The CODAS Data Storage Format
For .wdc Files
The structure of files saved to MMC or SD cards (.wdc files) are slightly different than files saved by acquiring data using WinDaq Acquisition software (.wdq files). The differences are noted here.
Header Element 5 (bytes 6-7)
Files recorded to MMC/SD from a stand-alone data logger product require that the data begin on a sector boundary in the memory card. Header Element 5 will contain 1536 (hexadecimal 600). MAX Channels is still 29, contrary to the table in the existing document. The extra header bytes are zero filled up to the fixed value of 8001 hexadecimal in Header Element 35 (bytes 1534-1535). See Header Element 5 in .wdq file.
Header Element 15 (bytes 40-43)
Indicates when the file was closed. The start time in element 14 (bytes 36-39) may be 0, in which case WinDaq computes it from the end time, file size, time interval between samples on a channel, and number of channels. See Header Element 15 in .wdq file.
Header Element 19 (bytes 56-59)
Instead of containing pretrigger and posttrigger points, contains a 32-bit number of data values per channel from the physical start of data to the place where the next data will be written. If a wrapround has occurred, this locates the oldest data in the file. See Header Element 19 in .wdq file.
Header Element 23 (byte 65)
Data bits 6 and 7 designate the circular recording state and are designated below. See Header Element 23 in .wdq file.
|7||6||Circular Recording State|
|0||0||Normal .wdq file|
|0||1||First pass through circular file|
|1||0||Other pass through circular file|
|1||1||Circular file properly closed|
When using Remote Controls in Stand-alone mode keep the following in mind:
- When Remote Start/Stop is enabled in stand-alone mode, a remote flag channel is allocated, automatically changing the per channel sample rate (i.e., it essentially adds another channel). For example, if the throughput rate is 14400 samples/second with 2 channels enabled, your per channel sample rate is 7200 samples/second. If remote storage is enabled with the two analog channels, the per channel sample rate would be 4800 samples/second.
- The remote flag channel is allocated at the end of the scanlist.
- If Remote Start/Stop is enabled, Remote Events will be placed in the remote flag channel; otherwise, it is embedded in the two LSBs of the first channel of the .wdc file.
- At offset 109, remote storage flag is configured as:
Bit Description 4 1 = enable event marker 5 1 = enable remote storage control 6 1 = negative event slope 7 1 = low true for remote storage control level
- The physical channel assignment for the remote flag channel is 0x49.
- The content of the remote flag channel is:
Low Byte: 0 = Escape, ignore the high byte
2 = The high byte is part of a time stamp
- Since a time stamp takes four bytes, each time remote storage is activated, it is required to acquire at least four samples before remote storage control flag is tested again. For example, if you are sampling at 0.1 Hz, you will have to wait 40 seconds before remote storage control flag is tested again.
- Remote storage and Circular memory are mutually exclusive.