4.5 Data System

4.5.1 Requirements, Characteristics, and Features

The LAN data system is a microprocessor based data processor and command system for the low energy charged particle experiment. The data system performs several functions for the experiment. It controls the sampling intervals and modes of operation of the data collection devices. The varying spin rates and telemetry rates of the host spacecraft (S/C) are accounted for. It also performs arithmetic and compression routines to maximize the amounts of information available. To provide flexibility, it processes serial data commands received from the host S/C.

The structure of the data system is that of a small dedicated computer. It is shown in block diagram form in Figure 4.33. The data system is composed of three 6" x 6" integrated circuits which are all radiation hardened 4000 series and 1800 series CMOS devices, packaged as flat-packs.

Figure 4.33 Data system block diagram

The data system requires the following voltages and currents:

The clock frequency is 1.0 MHz. The data system is non-redundant, excepting the S/C interfaces. 

4.5.2 Data System Software

The main program is a polling loop which tests for occurrence of 9 flags, as shown in Figure 4.34. Preference is given to those functions which require the least timing delay. The initialization routine starts the data system in an operations state. An interrupt routine allows a new operating program to be loaded in the event of certain hardware failures.

The main routine calls subroutines to load commands, output data, and generate control signals. Three data processing routines are called to perform summation, compression, and sorting functions. The data format is fixed, regardless of the S/C telemetry rate.

Figure 4.34 Data system software block diagram. Click here for larger version (pdf file).

Next: Chapter 4.5.3: Format