Fundamental Technologies Galileo Spacecraft Pages

EPD Commands

Also see Command Changes.

Source: Bob Moore, various dates

There are 256 command codes that are allocated to this experiment by JPL, not all of which are used. There are motor control commands and EPD commands.

Motor commands can cause the motor to:

1. Stop scanning.
2. Start scanning.
3. Set a new interval between steps.
4. Go in and out of the chicken mode. (The chicken mode keeps the telescope behind the shield much of the time.)
5. Have its controller read out its own ROM or RAM to check the memory contents.
6. Go into a modified scan mode. The modified scan mode allows only specified sectors to be scanned. The specified sectors are ground programmable.
7. Go into open and closed loop modes in case there is a problem with the position encoder.
8. Go into an emergency mode in which the motor attempts to go where it is commanded to go using the maximum amount of power available for each step.
9. Go into a fast scan mode in which motor triggers arrive every 2-2/3 seconds.
10. Go to any sector and stay there.
11. Respond to a set number of triggers and stop to debug a possible problem.
12. Make the next sector change CW or CCW.
13. Reset via software or a hardware clear.

The EPD commands will:

1. Turn the LEMMS power on and off.
2. Turn each of the 8 LEMMS amplifiers on and off.
3. Turn the A detector bias on and off.
4. Turn the J' detector bias on and off.
5. Set the bias at normal or high levels.
6. Turn the CMS electronics on and off.
7. Turn the TOF electronics on and off.
8. Turn the PHA on and off.
9. Turn the motor driver on and off (but not the motor controller).
10. Disable or enable the TOF logic conditions on the rate logic.
11. Turn the CMS analog electronics on and off.
12. Choose the 0 degree or 180 degree end of CMS.
13. Cause the CMS to use the 0 degree and 180 degree ends for alternate logical records.
14. Turn the instrument off and turn on heat generating loads.
15. Program all thresholds for the alarm status monitor function.
16. Override the priority system in the PHA so that it will disable the ROM in the PHA and substitute a canned priority that gets sent up with the command as data.
17. Interchange odd and even definitions for two packets in a logical record so that in case the spacecraft synchronization is not what it is expected to be, the instrument can be resynchronized.
18. Put the motor into an accelerated scan mode where the motor goes faster than normal. Triggers are sent to the motor every 8/3 second to get the motor to step at a faster rate to the sector designated as the end, stay there for 12 seconds and then come back.
19. Load the motor controller memory with one byte of instructions which will allow problems in the ROM to be patched around.

Eight-macro commands, which have not been defined yet, will be combinations of the commands that have been discussed. (Only four macros, specified 3/19/81, have been defined to simplify placing the instrument into a normal operating mode.)

The following list contains all of the Galileo EPD bus commands. Those commands preceded by an asterisk (*) are interactive commands. Those commands which have a second byte (bits 9-16) in addition to the op-code are data commands. The data symbol which represents the second byte can be one of 256 binary coded levels. Commands with op-codes less than 80 (hexadecimal) are destined for the EPD motor controller; commands with op-codes greater than 7F (hexadecimal) are destined for the EPD data system. Some of the commands which are executed by the data system also affect the motor controller; however, the internal communications between the motor controller and the data system do not involve the CDS bus or the EPD bus adapter. Commands listed with no mnemonic symbol are internal commands that do not involve the CDS.

Table 25. Galileo EPD Bus Commands

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Updated 5/10/04, T. Hunt-Ward
tizby@ftecs.com