Conventions
  -----------
  
  Mono Layer:  
                  _   _   _ 
                _/ \_/ \_/ \_
                 \_/ \_/ \_/


  Single Layer:

                    _   _   _    
                  _/ \_/ \_/ \_
                _/ \_/ \_/ \_
                 \_/ \_/ \_/



  Double Layer:                 
                        _   _   
                      _/ \_/ \_
                    _/ \_/ \_/
                  _/ \_/ \_/ \_
                 / \_/ \_/ \_/
                 \_/ \_/ \_/




  
   The chambers consistst out of single layers (a few), 2fold single
   layers (standard non-trigger type) and double layer (triger type) 
   layers.



   2fold-signle layers:

   2fold single layers are used to allow longuitudinally segmented 
   single layers in one module. For this purpose the signal from
   the inner sectors are transmitted to the module end by the use 
   of thicker wires:


   upper single layer:

         sect 1                    sect 6  

       --------------|           |-----------=================
       --------------|           |-----------=================
       --------------|           |-----------=================
       --------------|           |-----------=================

   
   lower single layer:

                        sect 5                     sect 2

       ==============------------|           -----------------
       ==============------------|           -----------------
       ==============------------|           -----------------
       ==============------------|           -----------------

  

   ( --- sensitive wire;   === thick wire used for signal transmission) 



  For the readout the channels inside the single layer should go 
  sequentially to the TDC: Neighbouring cells in the singel layer
  must go to adjacent ASD8 channels.
  Thus the first 16 channels of the lower single layer go to different
  ASD8 than the 16 channels of the upper layer: 
  
 
                                                                    ^    
              b1     b3     b5    b7    b9    b11    b13    b15     |
          b0     b2     b4     b6    b8    b10    b12    b14        |  z
       a1     a3     a5    a7    a9    a11    a13    a15            |
   a0     a2     a4     a6    a8    a10    a12    a14               |


   
   
  Since the different sectors see different rates also the HV supply
  of the upper and lower single layer must be different. 

               h2     h2     h3     h3    h2     h2     h2     h2
           h2     h2     h2     h2     h2     h2     h2     h2   
       h1     h1     h1     h1     h1     h1     h1     h1
   h1     h1     h1     h1     h1     h1     h1     h1   




   Trigger Layers:

   In case of the trigger modules the segmentation of the upper and
   lower single layer is the same. To have a geometrically  dense
   layer two modules with different segmentation must be glued together.
 
     
   To achive highest efficiency the two adjacent cells in z are ORed 
   to one trigger cell. The ORing is only possible if the channels
   occupy adjacent TDC channels. Thus the signal cabling is different 
   from the 2fold single layer case:

    order of signals on both ASD8s:
  
       z11    z15         a3     a7    a11     a15    b3    b7    b11    b15
    z9    z13          a1     a5     a9     a13     b1    b5    b9    b13   
       z10         z14    a2     a6    a10     a14    b2    b6    a10    
    z8          z12    a0     a4     a8     a12     b0    b4    b8   
 


  In order not to loose a complete chamber region in case of an HV
  trip the two single layers must be individually powered:

 
               h2     h2     h3     h3    h2     h2     h2     h2
           h2     h2     h2     h2     h2     h2     h2     h2   
       h1     h1     h1     h1     h1     h1     h1     h1
   h1     h1     h1     h1     h1     h1     h1     h1   



   
  HV grouping:

  Every standard HV group should have 16 channels. This is the smalles
  group which can be connected from outside the chamber in case of a 
  shortage.
 
  


  Standard and special Modules

  The standard Hera-B OTr honeycomb module has 4x32 5mm cells or
  4x16 10mm cells.
  There is large amount of modules with less cells. Actually all 
  possible cell numbers appaer. The new HV board design should   
  reflect this situation by an adequat modularity. In addition
  to HV boards have 2x16 channels also a board with 2x8 channels
  is sugested.