Siemens SIMATIC S7-200 - Token Rotation Comparison; Token Rotation Time Versus Number of Stations and Amount of Data at 9.6 Kbaud

Setting Up Communications Hardware and Network Communications
7-45
S7-200 Programmable Controller System Manual
A5E00066097-02
Token hold time (T
hold
) = (128 overhead + n data char)  11 bits/char  1/baud rate
Token rotation time (T
rot
) = T
hold
of master 1 + T
hold
of master 2 + . . . + T
hold
of master m
where n is the number of data characters (bytes)
and m is the number of masters
Solving for the token rotation time using the example shown above, where each of the six
masters has the same token hold time, yields:
T (token hold time) = (128 + 4 char)  11 bits/char  1/9600 bit times/s
= 151.25 ms/master
T (token rotation time) = 151.25 ms/master  6 masters
= 907.5 ms
(One “bit time” equals the duration of one signaling period.)
Figure 7-30 Formulas for Token Hold Time, Token Rotation Time, Using NETR and NETW
Token Rotation Comparison
Table 7-12, Table 7-13, and Table 7-14 show comparisons of the token rotation
time versus the number of stations and amount of data at 9.6 kbaud, 19.2 kbaud,
and 187.5 kbaud, respectively. The times are figured for a case where you use the
Network Read (NETR) and Network Write (NETW) instructions with the CPU or
other master devices.
Table 7-12 Token Rotation Time versus Number of Stations and Amount of Data at 9.6 kbaud
Bytes Transferred
Number of Stations, with Time in Seconds
Bytes
Transferred
per Station at
9.6 kbaud
2
stations
3
stations
4
stations
5
stations
6
stations
7
stations
8
stations
9
stations
10
stations
1 0.30 0.44 0.59 0.74 0.89 1.03 1.18 1.33 1.48
2 0.30 0.45 0.60 0.74 0.89 1.04 1.19 1.34 1.49
3 0.30 0.45 0.60 0.75 0.90 1.05 1.20 1.35 1.50
4 0.30 0.45 0.61 0.76 0.91 1.06 1.21 1.36 1.51
5 0.30 0.46 0.61 0.76 0.91 1.07 1.22 1.37 1.52
6 0.31 0.46 0.61 0.77 0.92 1.07 1.23 1.38 1.54
7 0.31 0.46 0.62 0.77 0.93 1.08 1.24 1.39 1.55
8 0.31 0.47 0.62 0.78 0.94 1.09 1.25 1.40 1.56
9 0.31 0.47 0.63 0.78 0.94 1.10 1.26 1.41 1.57
10 0.32 0.47 0.63 0.79 0.95 1.11 1.27 1.42 1.58
11 0.32 0.48 0.64 0.80 0.96 1.11 1.27 1.43 1.59
12 0.32 0.48 0.64 0.80 0.96 1.12 1.28 1.44 1.60
13 0.32 0.48 0.65 0.81 0.97 1.13 1.29 1.45 1.62
14 0.33 0.49 0.65 0.81 0.98 1.14 1.30 1.46 1.63
15 0.33 0.49 0.66 0.82 0.98 1.15 1.31 1.47 1.64
16 0.33 0.50 0.66 0.83 0.99 1.16 1.32 1.49 1.65