Hub SN28 IPMC scope tests:

Picture Test 1
---------------
This is a scope plot of the DCDC startup control.
Channel B: The collector of Q2951, which sends the RAMP-UP 
           signal to the DC converters.
Channel C: U2954 2-3: Enable signals to the DC converters
Channel D: The U2951/U2952/R2953 junction.

Scope setting are:
- 5V per division
- 2S per division

- Entire test was 20 seconds long.
- Far left side shows noise on all lines with power off.
- Next, the ATCA Enable switch is thrown on the benchtop power 
  supply. Noise drops off, Q2951 collector goes high.
- Handle Switch thrown. Q2951 goes low. U2951 outputs to 2952,
  which then outputs to U2953.
- Far right side shows handle being opened and unit powering 
  down.


Picture Test 2
---------------
This is a plot of the IPMC module during Power Supply startup.
Channel A: The Handle Switch input to the IPMC (p 224)
Channel B: The Payload Enable signal from IPMC to ISO_12V (p 225)
Channel C: Alarm In from Power Entry (p 226-7)
Channel D: IPMBus B Data (p 243)

Scope settings are:
- 5V per division
- 400ms per division

- Total screen time is 4.8S
- Far left shows board inserted in the slot. Power Entry is on, and
  IPMC_3.3V and (presumably) CNST_5.0V are active.
- The ATCA Handle is closed, sending Pin 224 low.
- Roughly 3/4 sec later, the Payload Enable to the ISO_12V supply
  goes high.
- Channel D just shows chatter on one of the two IPMBus lines.