1. Range Measurement Unit Messenger Mercury Laser Altimeter Basic Familiarization

2. Basic Function RMULaser Fire Detector Returns Computer Timing Reference 5 MHz from S/C, redundant Note can use an internal 5 MHz source. 5

3. Measurement Information Generate Fire command –Rate:8 Hz (1, 6, and 10 Hz available) Range Gate –Independent open and close commands –Referenced to TimeZero –Multiple of 200 ns –TX is not masked by the Range Gate

4. Range Gate (cont’d) Default values for Range Gate –Open: 001000 16 –Close: 013000 16 –Units are 200 ns per count Defaults restored by either: –Hardware Power-on reset –Software Reset

5. Signal Returns Filter 1 Filter 3 Signal Filter 2 a b h g f e d c Note: Only one b-c per shot Up to 15 “little pulses” per shot

6. Events Input to the RMU Six Events –TX_Leading –TX_Trailing –Pulse_B –Pulse_C –Pulse_AEG –Pulse_DFH t PW = Not defined Lockout time = Not implemented

7. Noise Counters Four Noise Counters –NC BC –NC AD –NC EF –NC GH t PW  Not defined 16-bit Saturating Counters Dead Time < 0.01% Sampled and zeroed at RUPT

8. Event Counters Five Event Counters –TX –BC –“Little Pulses” AD EF GH t PW  Not defined 8-bit Saturating Counters Enabled when Range Gate is opened

9. RMU - CPU Timing 125 ms Cycle Start Range Gate Dump Data Interrupt CPU Done max Issue CMDs TimeZero

10. Measurement Information Return Pulses per Shot Number:First 15 to arrive Except High Threshold Channel 1 (one only) Pulse-pair Resolution:~ 1.5  s

11. Measurement Information Measurements for Each Return Pulse Resolution:2 ns, max Channels: –CH1:10 ns filter two points leading edge two points trailing edge –CH2:60 ns filter one point leading edge one point trailing edge –CH3: 270 ns filter one point leading edge one point trailing edge Channel stored:1st channel signal to arrive Lockout and Channel ID provided by Detector Electronics

12. Shot Timing - Big Picture 125 ms Cycle Start Fire Range Gate Start Return Returns TimeZero

13. Range Gate Returns Returns arrive randomly Process first 15 returns to arrive within Range Gate Pulse-pair resolution ~ 1.5  s ~1.5  s

14. A Return Pulse VLVHVLVLVLVHVLVL b a c d e f g h 10/60 1/10 10/200 250/500 TimeZero

15. Event Time Stamping System View DetectorSpacecraft RMU Event 5 MHz CPU

16. Event Time Stamping RMU View FPGAEvent 5 MHz TOF10 bits @ ~0.4 ns/bit (fine timing) 23 bits @ 200 ns/bit (coarse timing) TOF = APL Time of Flight Microcircuit

17. Event Time Stamping System View DetectorSpacecraft RMU Event 5 MHz CPU

18. Event Time Stamping RMU View FPGA Event 5 MHz TOF10 bits @ ~0.4 ns/bit (fine timing) 23 bits @ 200 ns/bit (coarse timing) TOF = APL Time of Flight Microcircuit

19. Event Time Stamping TOF View Event 5 MHz TOF10 bits @ ~0.4 ns/bit (fine timing) TOF = APL Time of Flight Microcircuit TOF outputs time from Event to the next rising edge of 5 MHz

20. Calibration Mode Internally generated pulses can be sent to the TOF which are based on the 5 MHz clock. –0 ns: not guaranteed to work, STOP may precede START –200 ns: most important and guaranteed to work –400 ns: not guaranteed to work, STOP-START may exceed 400 ns. Available on –TX trail –Each edge of “little pulses”

21. 1 Hz Synchronization Upon power-up or Software Reset, the RMU will free run and ignore the 1 Hz signal If 1 Hz synchronization is enabled, then the 1 Hz signal will force the RMU to immediately lock to the 1 Hz. This may result in rapid pairs of FIRE and RUPTs

22. Babble Bit The software is not supposed to pulse either the READ or WRITE lines after TimeZero and before RUPT. If this relationship is not met, then the BabbleBit is set, indicating a cycle slip. The BabbleBit may be cleared only be a power-on reset or a software reset. There is no lockout.

23. Reseting the TOF-As The TOF-A’s are reset with either a hardware power-on reset or a software reset. The TOF-A’s do have a lockup mode. Optionally, the TOF-A’s may be reset after every TimeZero by CYCLERESET by a command to the RMU. The effect of a reset on a TOF-A is a mystery, it may alter the state of the PLL.

24. Command Registers All command registers are Read/Write All command registers are also included in the telemetry packet.

25. Disabling the RMU The only way to disable the RMU is to turn off the power. There is no disable for LaserFire There is no disable for RUPT

26. Little Pulse Lockouts and Timers The leading edge of a “little pulse” will lock out the other channels. Only a corresponding trailing edge will be permitted to occur. There is a 2  s timer. –If the corresponding signal does not arrive, the state machine is recycled. Three bit, “one-hot” Channel ID –For a time out, Channel ID = 000 –More than 1 bit set is an error detection mechanism. These may occur as they can not be designed out.