Cassini MIMI Investigation at Fundamental Technologies

 Historical MIMI Memos and Notes

Data Processing Unit

J. Dandouras, MIMI team meeting, October 1994

MIMI DPU Analog Electronics I/F Test

A. DPU Housekeeping Board I/F

• Read/write in HSK registers: OK
• Read value from ADC (interrupt driven): OK

Note: For read operations in some registers, the timing diagrams show that there are not adequate margins. We thus decided to add a waiting state (in the ACTEL implemented waiting state generator) for addressing the HSK board and having 4 instead of 3 waiting states.

B. DPU CHEMS Processing Board I/F

• Read/write in CHEMS registers (accumulators and PHAs): OK

General remark: Many DPU signals are very noisy. This is due to the wire wrapping technique used in the breadboard: parasitic capacitance and inductance, high cable lengths, cross-coupling between cables, no ground and power planes. Situation is anticipated to improve significantly with the Engineering Model (PCBs technique). For the breadboard, some corrective actions were taken: insertion of some additional decoupling capacitors and replacement of ACT (rapid) tranceivers with HC (slower) tranceivers.

MIMI DPU Turntable I/F Test

• Test of the 4 motor power modes: OK
• Test of the 2 directions of rotation: OK
• Test of different rotation speeds: OK
• Read of the absolute position (interrupt driven): OK
• Potentionmeter read-out (through the HSK ADC): OK

Notes:

1. A Schmitt trigger has to be added on the Absolute_Position and on the +5V_Echo signals.

2. The ACTEL implemented I/F will be re-programmed, in order to avoid a sudden stop of the turntable in case of a watchdog reset of the DPU.

3. Same general remark as for the Analog Electronics I/F concerning noise of some DPU signals.

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