The Galileo Energetic Particles Detector

Galileo EPD Handbook

Chapter 2. EPD Software

EPD SBAND Mission Software Requirements (continued)

Source: S. Jaskulek, various dates

CDS-Produced EPD Telemetry Record (continued)

RECORD RATE CHANGE COVERAGE SCIENCE PACKET HEADER

Figure 3. EPD3 RRCC Mode Packet Header

Time Included - This bit indicates if the time filed contains information. For the Record Rate Change Coverage data, time is always included.

Application ID - This 7-bit field generated by the CDS for all packets, and is used to identify the source of the data.

Size - This 9-bit field indicates the number of data bytes included in the packet.

Sequential Number - This 7-bit counter is incremented for each new EPD packet created.

Time - This 32-bit value will contain time reference data whenever the "Time Incl." flag is set. The format is "R-R-R-mf." This is the 24 least significant bits of the S/C RIM counter + spacecraft minor frame clock.

A more complete description of the header contents is contained in GLL-3-280, Rev. D, Appendix D.

RT RATE SCIENCE PACKET DATA

Each rate channel bin is represented by a 9 bit number. The format of the bins in the telemetry packets is shown below:

Figure 4a. EPD2, Map1 Rate Packet Data Format

Figure 4b. EPD2, MAP2 Rate Packet Data Format

Note: These tables were revised to match the actual CDS readout pattern (vs. what the EPD had originally requested; 2/6/96).

HOUSEKEEPING AND STATUS DATA

This area contains the information necessary to monitor the health of the instrument. All of the information in this field will be collected and formatted by the EPD and provided to the CDS for direct inclusion in the telemetry packet. There are several types of information included here (1 byte each):

1. HV Monitor - This byte is copied from the EPD analog housekeeping subcommutated data. It represents the measured output level of the high voltage supply. The binary to engineering unit conversion is the same as is used for the subcom HV monitor value. This value is included in the S/C engineering channels as S-1673; it does not appear as part of the EPD telemetry record.
2. Subcom Index - This byte identifies which subcom parameter is reported in the Subcom Value byte. Value will range from 0 to 91; these values correspond directly with the MOD91 subcom-based housekeeping used in the HGA and record mode software.
3. Subcom Value - This value contains a subcommutated byte from the original EPD subcom array. A (new) command option will provide the ability to freeze the subcom on a particular parameter.
4. Opcode - This byte contains the opcode of the last command executed by the EPD. This is the same status channel as is reported in the HGA and record mode software.
5. CMS PHA Block Entry Pointer - This 5-bit pointer indicates where in the CMS PHA readout sequence the data was taken (see below for details). The pointer will be maintained by the EPD software and passed to the CDS.
6. Status Bits - This is a collection of bits from the instrument:

   MSB	[1] Motor Scan Error Flag [1] Combined Error Flag {Power Monitor Flag + Bus Adapter Parity Error Flag + Resync Flag]} [1] Subcom mode {0=rotating, 1=fixed} Note: This is a new PhaseII feature. [1] Motor Direction Flag [0=CCS, 1=CW] {sampled at the beginning of each new science record} [1] Motor Centerline {sampled at the end of each science record}
   LSB	[3] Motor Position {sampled at the end of each science record}

When the 10 bps telemetry rate is being used, the motor will complete 3 complete cycles per science record. This provides uneven coverage to the end sectors, but this can be compensated for on the ground if the motor stepping pattern used in each science record is known.  The motor direction flag will be used by the ground processing sofware to determine if the stepping pattern is {0-5, 6-1, 0-5} or {6-1, 0-5, 6-1}.

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