\multirow{2}{*}{"01000"} & \multirow{2}{*}{Spike number} & Number of spikes (pulses narrower than 40~ns) detected at the timing trigger input\\\hline
\multirow{3}{*}{"01001"} & \multirow{3}{*}{Idle time} & Total time length, that the readout FSM waited in the idle state (with granularity of 10~ns)\\\hline
\multirow{3}{*}{"01010"} & \multirow{3}{*}{Wait time} & Total time length, that the readout FSM waited in the wait states (with granularity of 10~ns)\\\hline
- \multirow{2}{*}{"01011"} & \multirow{2}{*}{Total empty channels} & Number of empty channels since the last reset signal\\
+ \multirow{2}{*}{"01011"} & \multirow{2}{*}{Total empty channels} & Number of empty channels since the last reset signal\\\hline
+ \multirow{2}{*}{"01100"} & \multirow{2}{*}{Readout time} & Total time length, that the readout occured (with granularity of 10~ns)\\
\hline
\end{tabularx}
\caption{Debug information word bitmap.}
The debug words sent with DAQ can be accessed also via slow control registers (see Table \ref{tab:tdcStatusReg1} and Table \ref{tab:tdcStatusReg2}).
\newpage
+
+\subsubsection{EPOCH Counter}
+
+As the global coarse counter has the time limit of \~10~us, a overflow counter
+(EPOCH counter) is implemented in order to increase the measurement range. The
+data format of the \textbf{\textit{EPOCH Counter}} word is shown below:
+
+\begin{table}[h]
+ \centering
+ \begin{tabular}{|W{1.275cm}|W{7.225cm}|W{5.1cm}|}
+ \hline
+ 3 bits & 17 bits & 12 bits\\
+ "011" & reserved & EPOCH Counter\\
+ \hline
+ \end{tabular}
+ \caption{The data format of the \textit{EPOCH Counter} word.}
+ \label{tab:tdcReservedWord}
+\end{table}
+
+The EPOCH counter is first designed with 12 bits increasing the total
+measurement range up to \texttildelow41,9~ms. For each channel an individual EPOCH
+counter is implemented and they are incremented, when the coarse counter
+wraps around. The value of the EPOCH counter is kept in a register before it
+is written in the channel memory. It is only written in the memory, if a time
+measurement takes place after the last increment of the EPOCH counter. The
+EPOCH counter word is written in the memory only once per channel for each
+increment, thus saving bandwidth. In order to be on the safe side and not
+overflow the EPOCH counter, the readout trigger frequency can be set minimum
+to 24~Hz.
+
+
\subsubsection{RESERVED}
The data format of the \textbf{\textit{reserved}} word is shown below:
\begin{tabular}{|W{1.275cm}|W{12.325cm}|}
\hline
3 bits & 29 bits\\
- "011" & reserved\\
+ "000" & reserved\\
\hline
\end{tabular}
\caption{The data format of the \textit{RESERVED} word.}
& & 31-24 & reserved\\ \hline
\multirow{2}{*}{0x8f} & \multirow{2}{3.5cm}{Release Number} & 23-0 & Number of release signals sent\\
& & 31-24 & reserved\\ \hline
- \multirow{3}{*}{0x90} & \multirow{3}{3.5cm}{Channel Scaler} & 23-0 & Number of hits detected by a channel. Channel number is controlled with register 0xc4\\
+ \multirow{3}{*}{0x90} & \multirow{3}{3.5cm}{Readout Time} & 23-0 & Total time length, that the readout occured (with granularity of 10~ns)\\
+ & & 31-24 & reserved\\ \hline
+ \multirow{3}{*}{0x91} & \multirow{3}{3.5cm}{Channel Scaler} & 23-0 & Number of hits detected by a channel. Channel number is controlled with register 0xc4\\
& & 31-24 & reserved\\ \hline
\end{tabularx}
\caption{The status registers of the TDC. (Continue)}