We've found two discrepancies between the ADC/DAC channel assignment document T1100472 and the end station ISC  wiring document D1100670. After some discussion, we decided that the right way to proceed is to change the channel assignment in the model and update T1100472. The model was already updated but the document is yet to be done. Physical wiring was not changed at this time.

1: CM boards fast readback channel assignment

We have two CM boards at the end station, one for PLL and one for PDH, and the fast readback looked like they were swapped.

According to the wiring diagram, the first CM board is PLL and the second one is PDH. Which means that the PLL CM board uses the first ADC DB9 input for AA for ADC 1 and PDH uses the second. Physical wiring as well as slow control follows this convention.

OTOH, the channel assignment document says that DB9_1 for ADC1 is used by PDH and DB9_2 is PLL. h2iscey model follows this.

We decided to change the channel assignment so everything agrees with everything.

2: Misc. diodes DC fact readback channel assignment

There are two kinds of photodiode DC output, one is the DC of the legacy iLIGO RF diode and the other is the output of generic diodes (e.g. PDA 100A) via the new aLIGO generic tabletop interface.

In the wiring diagram, the legacy output is not connected to the fast readback at all. The generic interface is connected to the third DB9 of AA input for ADC1.

In the channel assignment document, DB9_3 for ADC1 is used by the iLIGO RF diode (PDH_DC) and the generic interface uses DB9_4.

We decided to leave the physical wiring alone, but swap the channel assignment (i.e. DB9_3 for generic and DB9_4 for legacy) in the model.

Each DB9 holds up to four channels, and before the model change DB9_3 and DB9_4 used to hold a total of 4 channels.

After the change, each of these have 4 channels.

In DB9_3, PD1 is the new channel H2:ISC-ALS_EY_REFL_PWR_MON (which is a diode in the Hartman WFS path). Three old channels that already existed  were shifted by one slot (PD2=red power monitor, PD3=green power monitor, PD4= PLL DC power).

In DB9_4, we have four channels (PDH DC, AUX1, AUX2 and AUX3 in this order). AUX channels are new (but PDH DC was not available in reality anyway, because there was and is no physical connection to the AA, it was/is only connected to Beckhoff). We need another cable going from the field to the AA chassis to actually use these four channels.