Appendix 15. Validity Checks of LAN Data Stream

 

 

Processing the LAN data received on the Experiment Data Record (EDR) tapes from JPL must include validity checks as one of the first operations. Quality checks of the data reception and decoding by JPL are included in the EDR headers. Quality checks of the LAN data itself are included in the status preamble and status trailer words of the LAN logical record.

 

The status preamble words generally refer to the state of the spacecraft and the LAN subsystems. Changes in these status words usually affect an entire 4-format logical record. The status trailer generally reports spin-by-spin data quality.

 

The LAN data stream must be validated first on a 4-format basis, followed by a spin-by-spin validation within a 4-format period. The following order is suggested for the data reduction algorithm.

 

Format Validity Checks:

 

1. Power-On Telltale. This bit must be on during format zero and must remain on for valid data. Following the first appearance of the power-on bit, the rate and pulse height data are guaranteed valid after two 4-format pulses have passed (MFSA data after three 4-format pulses).

 

If the power-on bit disappears, indicating LAN has been turned off, the data will be valid through the last full spin pair prior to the last format which had a power-on bit.

 

2. ROM/RAM Mode. This bit shows whether the standard internal data processing program is operating. Data are not valid following a switch to RAM mode. After switching back to the ROM mode, validity is assured after the second 4-format pulse (third pulse for MFSA data).

 

3. Power-Down Telltale. Data are valid through the last full spin pair prior to the last format with valid power-up bit. Rate and PHA data are valid following power-up only after the appropriate subsystem power bits have been on for at least one full format (i.e., starting at the second appearance of the subsystem power-on bit). MFSA data will be valid after the second 4-format pulse at which both PHA power-on bit and the power bit for the appropriate analog subsystem have appeared. Rate and pulse height data should only be used in full spin pairs.