The Galileo Energetic Particles Detector
Galileo EPD Handbook
Chapter 1. Instrument Summary
Hardware Changes (continued)
Output High Voltage Reference
There will be a high voltage power supply in the TOF box that must be provided a reference. This reference signal tells the supply what level output voltage to generate. The data system will output a reference with 4 bits of resolution (16 possible levels); this digital information will be converted to an analog reference inside the supply.
The easiest way to do this would be to output 4 bits from the data system and provide them to the supply. Unfortunately, there are not enough unused I/O ports to do this; the spare I/O bits that are available are occasionally changed by the present software.
There are presently only 4 bits used on the data system's housekeeping mux I/O port (U59 of the data system: Q=1, N=1); the other 4 bits are spares (one is labeled HMUX 3, but is not used) and are already connected to spare motherboard pins. The problem with these spares is that each time the housekeeping multiplexer changes to another analog value (approximately every 5 seconds), the unused bits are set to zero. The new design, therefore, will use these bits as data inputs to a 4-bit latch on the HV converter. The clock line for this latch will be a spare bit on the motor controller board (power switch byte 3, bit 6: Q=1, N=3). (Even though this I/O port resides on the motor controller, it is operated off the data system microprocessor bus.)
Upon receipt of a high voltage reference command, the data system would check the new reference against an upper limit stored in software. If the value is within acceptable range, the 4 bit code corresponding to that level would be output via the spare bits on the housekeeping mux port to the high voltage converter input latch. The data system would then strobe the 4 bits into the latch via the spare motor controller I/O bit.
Because the housekeeping mux continuously sets the data bits to zero and the data system clears all I/O ports on initialization, we do not have to worry about setting the reference to zero on power-up. It will be necessary to clock this data into the latch via software prior to turning the high voltage power on. Addressing concerns in the other direction, power switch byte 3 is normally addressed one bit at a time, so the contents of the spare bit will not be modified by the current software except upon reset.
We will need to implement new commands in the instrument to accomplish these control functions. The details of these commands and the software needed to effect them will be discussed in a later section.
Continue: Convert HV Reference Digital/Analog Conversion
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Updated 8/23/19, Cameron Crane
QUICK FACTS
Mission Duration: Galileo was planned to have a mission duration of around 8 years, but was kept in operation for 13 years, 11 months, and 3 days, until it was destroyed in a controlled impact with Jupiter on September 21, 2003.
Destination: Galileo's destination was Jupiter and its moons, which it orbitted for 7 years, 9 months, and 13 days.