CUBIC uses one bilevel housekeeping channel ( SAC-B \ Housekeeping Bilevel Channel 00). This is an 8 bit bilevel status word (BL1) monitoring the most critical CUBIC experimental status indicators. Three of these bits are set by hardware so that the CUBIC ICP status can be monitored even when the ICP has halted; the remainder of the bits are set by the ICP. This data word is transmitted to the Telemetry Processor as 8 parallel digital bits. The bit assignments are shown in Table 17.
Table 17: CUBIC Bilevel Housekeeping Words
(Note: because of a wiring error in the spacecraft harness, the bit order of BL1 is reversed in the C&DH system. The bit assignments shown in Table 17 are the assignments as they appear at the groundstation and in the housekeeping data files. The bit assignments used in the flight software are reversed from what is shown here.) The Microprocessor Status bit is generated in hardware, based on activity on the LSB of the address bus. The Watchdog Status bit is generated in hardware by the watchdog circuit. The Reset Status bit is generated in hardware by the RESET line. The System Parameter Status bit is generated by the ICP, based on the status of the uploadable threshold values and other system parameters. Each of these values is stored in three memory locations by the ICP to guard against SEUs. The ICP compares the contents of these three locations during regular housekeeping checks and corrects any location found to differ from the other two copies of the same value. In the event that three different values are found during one of these checks, the System Parameter Status bit will be set and the suspect parameter will be reloaded with its default value stored in ROM. The DAC/Clock Voltage status bit monitors the settings of the DACs (most of which set clock voltages) by comparing the desired set point of each DAC channel with the value measured by the housekeeping. In the event of a discrepancy larger than that allowed by the appropriate ``Allowed Range'' value (see §4.5), the DAC/Clock Voltage status bit will be set. Operations will continue normally to prevent an error in the housekeeping from shutting down the experiment. Similarly, the Power Supply Status bit will be set if any power supply voltage deviates from its nominal value by more than the appropriate ``Allowed Range'' value, but will not affect experiment operation.