Readout
=======

Time to Digital Converter (TDC)
-------------------------------

.. figure:: tdc.png
    :figwidth: 70%
    :align: center

    TDC principle


When a channel crosses the threshold, the state of the counter is stored locally. If a channel has no enough current to cross the threshold before the end
of the measure it is lost. 

The counter is a 16 bits Gray counter (1 to 65000).


Analog Multiplexed (AMUX)
-------------------------
The counter is stopped and currents are integrated during a tacq. Then integrator outputs are memorized using a sample and hold circuit.
The readout always starts by reading the hit register which indicates channels that have crossed the threshold.
Three readout modes are available:

* AUTO: only memorized values in hitted channels are read.
* ALL: all analog values are read.
* SELECT: the user send a list of channels to read to the ASIC. This mode is useful for reading neighbor channels


ASIC 8 channels (8CH)
---------------------

This is an ASIC test mode for but it can be useful in case of trouble due to a readout problem or noise in the numerical signal.
8 integrator outputs are selected among 32 on 8 PADs. Channels are clustered by 4 and one is selected by programming to be connected
in continuous (whitout need of a readout sequence) to an output PAD.

.. figure:: 8channels.png
    :figwidth: image
    :align: center