## 4 Evaluation of Serial Bus Network System
### Discussion  
We compared our network system of 48 sensor platform LSIs with other sensor systems mainly used for tactile sensation. There are eight capacitance channels and capacitance-to-digital converters in each sensor platform LSI. In total, 384 capacitance channels and capacitance-to-digital converters are included in this network system. The average sampling frequency of these capacitance channels is 73.66 Hz, which is higher than most of the systems shown in Table 1. The length of the bus line is 2.4 m, which shows an ability to cover much larger areas. Since each sensor platform LSI can connect eight capacitive sensors, the network system can include 384 capacitive sensors.  
Assume that our network system has a scanning readout mode. We send a Send One Data Packet command to a specific sensor platform LSI, and the corresponding LSI receives this command and sends one data packet. Then, we receive this data packet, and send another Send One Data Packet command to the next LSI. According to this procedure, we scan all the 48 LSIs continuously. Assume that the Send One Data Packet command includes 32 bits of which eight bits are for the physical address, eight bits are for command identification and 16 bits are for CRC code. After 4B5B encoding, attaching a 9-bit preamble and a 5-bit stop code, the length of the command becomes 54 bits. Assume that there is a time interval between finishing receiving and starting to send, being four cycles of data or command transmission speed, and the data and command transmission speeds are the same as 61/64 MHz = 953.1 kHz. Then, sampling one LSI needs \(\left(254+54+4\right)/0.9531\) us = 331.55 us. The constant sampling frequency of all 384 capacitance channels is 62.84 Hz. This frequency is 10 Hz less than the average sampling frequency of our real network system because of the command overhead. On the other hand, the stimuli of all the 48 LSIs is a rare case in real application. We think the flexibility of our network system, enabled by the adaptation and event-driven functions as well as many configurable parameters, makes it a useful network system in robot applications, which we will confirm as a next step.  
Figure 16: Empirical distribution function of time interval values.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**System Structure** & \begin{tabular}{c} **Sensor Output** \\ **Digitization Place** \\ \end{tabular} & **Force Sensing Principle** & \begin{tabular}{c} **The Number of Capacitance** \\ **or Resistance Channels** \\ \end{tabular} & **Covering Area** & \
\begin{tabular}{c} **The Number of Analog-to-** \\ **Digital Converters (ADC)** \\ \end{tabular} & **Sampling Frequency (Ht)** & **Reference** \\ \hline \multirow{4}{*}{
\begin{tabular}{c} Tactile sensor array with \\ scanning readout circuitry \\ \end{tabular} } & \multirow{4}{*}{Off the sensor array} & \multirow{4}{*}{Cryactive} & 8\(\times\) 8 & 16\(\times\) 16 cm\({}^{2}\) & 1 (AD/T153) & 3 & [2] \\  & & 8\(\times\) 8 & 36\(\times\) 36 cm\({}^{2}\) & 1 (AD/CMSI) & n.a. & [3] \\  & & 16\(\times\) 16 & 22\(\times\) 22 cm\({}^{2}\) & 1 & 20 & [4] \\ \cline{2-7}  & & \multirow{4}{*}{Resistive} & 8\(\times\) 8 & 4\(\times\) 4 cm\({}^{2}\) & 1 (CMS/T5822) & 16 & [5] \\  & & 8\(\times\) 12 & 9\(\times\) 13 cm\({}^{2}\) & 1 (B/CMS/T5015) & n.a. & [6] \\  & & 8\(\times\) 8 & 25\(\times\) 25 cm\({}^{2}\) & 1 (B/CMS/T256) & 100 & [7] \\ \cline{2-7}  & & \multirow{4}{*}{Cryactive} & 12\(\times\) 16 & 39\(\times\) 16 cm\({}^{2}\) & 16 (AD/T147) & 25 & [11] \\ \cline{2-7}  & & & 114 & n.a. & 114 (MPL115A2) & 50 & [12] \\ \cline{2-7}  & & \multirow{4}{*}{of sensation} & \multirow{4}{*}{Cryactive or resistive plus temperature sensing} & 24 m & 73.66 (mean) & \multirow{4}{*}{This work} \\ \cline{2-7}  & & & 8\(\times\) 48 & & & 5.3 (vorsst) & \\ \cline{2-7}  & & & & & & \\ \cline{2-7}  & & & & & & \\ \cline{2-7}  & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of some tactile sensor systems with their performance.