Jurgen Engelfried
                                                        October 12, 1993

        Specification for CROS and RMH Readout Controllers
        ==================================================


                          1. Introduction
                          ---------------

The controller have to read out the equipments, and finally we need the data
on the RS485/DART (diff. TTL) cables to be transported to the DM115/DC2 in the
VME crate. The following conditions have to be meet, given by the overall
trigger and data aquisition system:

  1) Online deadtime <30usec. The frontend modules have to accept
     a new event in this time.

  2) Mean readout time per event <100usec. With buffers in readout controllers
     we can stretch the readout time by a factor of 3.

Each stream and/or each readout controller should produce a header (or trailer)
with an identifier, a wordcount and an event number. The event number will
be given to the controllers as a 4bit number on RS485, together with a strobe
signal which is the readout trigger. 


                    2. Expected Hits and Readout Time
                    ---------------------------------

CROS: DPWC: 4736 channels, 14 planes.    with  7 tracks ==> 100 Hits
      TRD : 3072 channels,  6 planes.    with  4 tracks ==>  24 Hits
      RICH: 2848 channels, 15 hits/ring. with  6 tracks ==> 100 Hits
                                                            --------
                                                            224 Hits

RMH:  PWC : 7680 channels, 12 planes.    with 10 tracks ==> 120 Hits
      LPWC: 2628 channels,  7 planes.    with  4 tracks ==>  28 Hits
                                                            --------
                                                            148 Hits


 Readout time: 5 Hits/usec ==>  44.8usec for CROS, 29.6usec for RMH

With this, CROS is over and RMH is near the 30usec boundary. This means,
we have to forsee to read out the systems with more than one readout 
controller (for CROS: split wire chambers and RICH/TRD).


                     3. Different Possibilities
                     --------------------------

To fulfill all the requirements, we have the following possibilities:

  1) The Readout Controller (successor of BIS.45056 and RMH equivalent) 
     is reading out and converting directly to RS485/DART without any 
     buffer in 16bit words. We need 2 streams for each CROS and RMH to have 
     a readout time <30usec. The Controllers have to receive the event number 
     and put it in a header or trailer. If the number of 16bit words is odd,
     the controller has to send an additional dummy word. After all
     data of one event are send, the Controller has to issue a 
     EOR (end-of-record) signal. 

  2) The Readout controller is reading out and converting directly in
     ECLine (FERA compatible). The data will be pushed into a DYC+, which
     has a 16kByte multi-event buffer, can receive the event number, sends
     the EOR and packs the data in 32bit words. Several DYC+s can be chained 
     to build one stream. If the DYC+ takes care of an odd number of 16bit
     words is not yet known.

  3) The Controller has to combine the functions described in 1) and 2) by
     itself.


                             4. Proposal
                             -----------

I propose the build the Controller with ECL output (possibilty 2), pushing
data in a DYC+, which will take care of buffering and event number handling.
The controller has only to receive a readout trigger and has to provide
a "BUSY" signal during the actual readout.
This system has the following advantages:

  1) The DYC+ is used by several DART experiments. A prototyp will be
     tested this month.
  2) The DYC+ is cheap ($100).
  3) We might use the DYC+ if we have to read out more than 40 CAMAC words
     for each event.
  4) The controllers itself are simpler.
  5) We can combine all CROS and RMH into one stream.



The specifications for the RS485/DART, the ECLine input for the DC2, and
the event number are given in the appendix.