\documentstyle[11pt,a4wide]{article}
\title{Eurogam VXI line usage}
\author{Ian Lazarus following discussion between:\\
Alphonse Richard\\
Ian Lazarus\\
Christoph Ender\\
Patrick Coleman-Smith\\
John Alexander}
\date{July 1990}
\begin{document}
\maketitle
\section{Introduction}
This document describes my understanding of the conclusions of a meeting
between engineers involved in Eurogam from UK, France and Germany held at
Daresbury on 16th July 1990. The paper under discussion which contains much
more detail was produced by Alphonse Richard (dated 13/7/90) after a
meeting held between French
engineers in Paris on 8th June who tried to cover the needs of
 {\em all} French VXI
instrumentation for nuclear structure physics, not solely Eurogam.
 
Where I refer to changes, they relate to the proposal mentioned above, 
{\em `Utilisation des Lignes VXI'} by Alphonse Richard dated 13/7/90.
 
\newpage
\section{VXI lines}
\subsection{Local Bus}
\begin{itemize}
\item LBUS0 Supplementary analogue sumbus 1 {\em agreed, unchanged}
\item LBUS1 Supplementary analogue sumbus 2 {\em agreed, unchanged}
\item LBUS2 Analogue inspection line 1  {\em agreed, unchanged}
\item LBUS3 Analogue inspection line 2  {\em agreed, unchanged}
\item LBUSA4 RENin   LBUSC4 RENout  (Readout ENable daisy chain) {\em agreed,
unchanged}
\item LBUS5 Voltage inspection line {\em NOT AGREED, see note 1} \dag
\item LBUS6 Contr\^{o}le des fen\^{e}tres {\em NOT AGREED, see note 2} \dag
\item LBUS7 not allocated                                          \dag
\item LBUS8 Event Number {\em agreed, but see note 3}              \dag
\item LBUS9 Event Number {\em agreed, but see note 3}              \dag
\item LBUS10 Event Number {\em agreed, but see note 3}             \dag
\item LBUS11 Event Number {\em agreed, but see note 3}             \dag
\item LBUS12 Reserved (Anti-Compton veto in Eurogam)               \dag
\item LBUS13 Reserved (Anti-Compton veto in Eurogam)               \dag
\item LBUS14 Reserved (Anti-Compton veto in Eurogam)               \dag
\item LBUS15 Reserved (Anti-Compton veto in Eurogam)               \dag
\item LBUS16 Reserved (Anti-Compton veto in Eurogam)               \dag
\item LBUS17 Reserved (Anti-Compton veto in Eurogam)               \dag
\item LBUS18-35 not allocated.                                     \dag
\end{itemize}
\subsection{ECLTRG 0-5}
\begin{itemize}
\item ECLTRG0 Validation 1 {\em agreed, unchanged}
\item ECLTRG1 Synchronisation of triggers for test mode {\em agreed,
unchanged}
\item ECLTRG2 Inhibit (D size) {\em agreed, unchanged}
\item ECLTRG3 Logic inspection line 1 {\em agreed, unchanged}
\item ECLTRG4 Logic inspection line 2 {\em agreed, unchanged}
\item ECLTRG5 Validation 2 {\em agreed, unchanged}
\end{itemize}
\subsection{TTLTRG 0-7}
\begin{itemize}
\item TTLTRG0 End of coding {\em agreed, unchanged}
\item TTLTRG1 End of readout {\em agreed, unchanged}
\item TTLTRG2 Transfer all scalers to shadow registers. {\em agreed,
unchanged}
\item TTLTRG3 Clear {\em agreed, unchanged}
\item TTLTRG4 Go/Stop {\em agreed, unchanged}
\item TTLTRG5 Event reject {\em agreed, unchanged}
\item TTLTRG6 Validation 3 {\em agreed, unchanged}
\item TTLTRG7 Inhibit (C size) {\em agreed, unchanged}
\end{itemize}
\subsection{STAR lines}
\begin{itemize}
\item STARX Fast trigger {\em agreed, but see note 4}
\item STARY Fast trigger {\em agreed, but see note 4}
\end{itemize}
\subsection{Sumbus}
\begin{itemize}
\item SUMBUS {\em agreed, unchanged but see note 5}
\end{itemize}
\subsection{VME lines}
VME lines are used for setup, executing normal VME cycles, and for readout in
a slightly non-standard method defined in a separate document.
\subsection{Other Lines}
All lines in this section are as defined in the VXI specification
\begin{itemize}
\item CLK10 
\item CLK100
\item SYNC100
\item MODID(00-12)
\end{itemize}
 
\section{Notes}
These notes describe changes made and reasons for the changes.
\subsection{Note 1}
It was not agreed that a third analogue inspection line must be defined for
measuring voltages. It was suggested that 2 are enough, and that if any more
than 2 analogue signals need to be measured simultaneously then on card ADCs
with VME readout should be used. It was agreed that the Eurogam slot 0 card
will have a strap to connect its slow ADC to either an analogue inspection
line or to LBUS5 (voltage inspection line) in case LBUS5 is reallocated.
\subsection{Note 2}
It was not agreed to allocate a VXI local bus line to window adjustment since
the adjustment can be made using the logic inspection lines. It was
agreed that we will explain the two methods to the physicists, and only if
there is a strong
preference for the analogue method would the line could be allocated.
(The UK physicists expressed no strong preference for either method when
asked.)
\subsection{Note 3}
These lines were changed from TTL to single ended ECL since they are sent with
the validation signals, 2 of which are ECL. ECL will also introduce less
backplane noise than TTL during analogue processing. It is not agreed whether
we use these lines in 2 pairs as proposed or use all 4 of
them with validation to
identify the event and then use VME address lines to select which of the 16
possible events will be read. (VME address lines can also be used during local
bus readout if a VME cycle precedes/accompanies local bus readout.
\subsection{Note 4}
STARX and STARY were changed such that both are usable in either direction.
Thus the `D\`{e}cision logique' usage and the `Trigger Rapide' usage is
possible on one line  or on two lines. In Eurogam it is possible (with coaxial
detectors) to make each Ge card handle one pentagon, so the STARX/Y line could
represent a hit in a certain pentagon. Alternatively, with two mixed detector
types in the same crate, we might want to introduce slightly different fast
trigger signals or a very fast validation. 
\subsection{Note 5}
Note that the proposal limits the VXI SUMBUS to --1.6~Volts whereas the VXI
specification allows $\pm 3$~Volts
\subsection{Other comments}
It was suggested that we could introduce classes of conformance so that all
signals in class 1 {\em must} be used as specified or left alone; those in
class 2 should be used as specified if possible, but may be re-allocated for a
good reason, for example to gain lines for local bus readout. All the signals
mentioned in this document would be class 1 signals except for Voltage
inspection (LBUS5), Contr\^{o}le des fen\^{e}tres (LBUS6),
Event number (LBUS8-11) and Anti-Compton vetos (LBUS12-17)
allowing LBUS5-LBUS35 to be used for local bus readout in a future system.
These class 2 signals are denoted in the list by the \dag symbol.
 
I believe that these lines should remain in class 2 at least until we have a
working VME readout scheme with a satisfactory data throughput. At this point
we can judge whether it is worth continuing to regard these lines as class 2
to facilitate an easy upgrade to Euroball which will use local bus readout
anyway or whether we can say that Eurogam will never require readout faster
than the measured VME rate and thus that these lines may be exclusively
defined as proposed.
\end{document}