\subsection{Backplane}

To connect the modules to the microprocessor, many pins need to be connected
straight through. For this purpose a backplane was chosen where DIN41612
connectors can be used. These connectors were chosen for their large pin count
(96 pins) and their availability. The backplane connects all 96-pins straight
through. With the 6 outer left and right pins connected for VCC and ground
as can be seen in Figure \ref{fig:schem_back_conn}.

\begin{figure}[H]
	\includegraphics[width=\textwidth, angle=0]{schem_pdf/backplane_conn.pdf}
	\caption{Layout of the DIN41612 Connectors on the Backplane}
	\label{fig:schem_back_conn}
\end{figure}

\subsubsection{Termination resistors}

In constrast to other systems using this backplane no termination resistors
were used. This makes the bus more prone to refelctions, however these were not
a problem during development with the maximum transmission rate of 1MHz, as can
be seen in the sample recording in Figure \ref{fig:reflex}

\begin{figure}[H]
\begin{tikzpicture}
	\begin{axis}[
		ylabel=Voltage on MS1,
		xlabel=Time,
		grid=both,
		xmin = -0.000001,
		xmax = 0.000002,
		minor tick num=5,
		width=\textwidth,
		height=0.25\textheight] 
		
		\addplot table [x=t, y=c1, col sep=comma, mark=none] {meas/20200319reflexions.csv};
	\end{axis}
	\end{tikzpicture}
	\caption{Measurement at around 1MHz bus clock on MS1}
	\label{fig:reflex}
\end{figure}

The ripple  seen in Figure \ref{fig:reflex} is most likely due to
the sample rate of the Oszilloscope, which is around 10Mhz after an average
filter has been applied. The measurement was performed on the finished project
with all cards installed.

\subsection{Case}

The case for the backplane was provided by the hackerspace and is meant for
installation in a rack. The case is meant for installation of cards in the
EUROCARD format, therefore all modules were built by this formfactor.

\begin{figure}[H]
	\includegraphics[width=\textwidth, angle=0]{pics/case}
	\caption{The case with installed backplane}
	\label{fig:case}
\end{figure}