8-2
Section
Communications Cycle Time
118
8-2-2 Inactive Data Links
The following equations are used to calculate the communications cycle time
when the data links are inactive. (The communications cycle time will vary some-
what depending on the baud rate and the conditions at that particular time.)
Wired Networks
Baud rate
Equation
2 Mbps
600
×
B + 110
×
C + 320
×
D + 4
×
E + 2,290 (
µ
s)
1 Mbps
1,150
×
B + 150
×
C + 360
×
D + 8
×
E + 2,690 (
µ
s)
500 Kbps
2,260
×
B + 230
×
C + 440
×
D + 16
×
E + 3,490 (
µ
s)
Optical Ring Networks
Baud rate
Equation
2 Mbps
(fixed)
Token Ring Mode
1,740
×
B + 450
×
C +1,100
×
D + 4
×
E + 2 x F + 3,000 (
µ
s)
Token Bus Mode
1,300
×
B + 110
×
C + 320
×
D + 4
×
E + 2 x F + 1,800 (
µ
s)
Note B: Number of polled nodes per communications cycle
(value specified in the network parameter)
C: Number of nodes connected to network
D: Number of nodes that send messages during the
communications cycle
E: Total number of bytes in messages transmitted during the
communications cycle
F: Extra communications time for long-distance cable connections.
If L is the cable length in km, then F = 7
×
L
µ
s for H-PCF cable and
F = 5
×
L
µ
s for GI cable.
Communications conditions are as follows:
Type:
Wired
Transmission medium:
Twisted-pair cables
Baud rate:
2 Mbps
Network parameters:
Defaults
Max node address:
32
Polled nodes per comm cycle: 4
Event-frames per comm cycle: 35
Network configuration:
8 nodes
Nodes that send messages:
2 nodes
Bytes in all messages sent:
2,012
2 bytes
In this example, B to E in the equation have the following values.
B:
4
C:
8
D:
2
E:
4,024
The communications cycle time is thus as follows:
600
×
4 + 110
×
8 + 320
×
2 + 4
×
4,024 + 2,290 = 22,306 (
µ
s)
≅
22 (ms)
Calculation Example for
Wired Networks
