Calculating The Communication Time - Hivertec motionCAT Series User Manual

1.5 Calculating the Communication Time

The communication time is classified into:
⚫
Amount of time for a cyclic communication
⚫
Amount of time for one data communication
⚫
Total amount of time for a cyclic communication including data communications
<Abbreviations>
N: Number of connected local devices
B: Number of bytes of transmitted data (in case of two-byte data transmission: B = 2)
K: Transmission speed coefficient
Communication speed (Mbps)
(1) Amount of time for a cyclic communication
Communication time for one local device
Amount of time for a cyclic communication (μs) = (CT + 7.4) N
Example: Where the transmission speed = 20 Mbps, The number of local devices = 30
A cyclic communication time = (7.71 + 7.4) 30 = 453μs
(2) Amount of time for one data communication
Data communications are classified into the following two types:
⚫
When data is present in a response from the local device (variable-length data)
⚫
When data is absent in a response from the local device
Send time
Respond time: with response data
Respond time: without response data
Amount of time for one data communication (μs) = ST + JT + 7.4
Example 1: Time required for writing data to one register of a motion device, where the transmission
speed = 20 Mbps:
A write command (2 bytes) and register data (4 bytes), totaling 6 bytes, are transmitted to write the
data to the motion device register. There is no response data. (A response frame only)
Data communication time = (60.6+3.25)1 + 5.051 + 7.4 = 19.3μs
Example 2: Time required for reading data from one register of a motion device, where the transmission
speed = 20 Mbps:
A read command (2 bytes) is transmitted to write the data to the motion device register.
Response data consists of a read command (2 bytes) and register data (4 bytes), totaling 6 bytes.
A data communication time = (20.6 + 3.25) 1 + (60.6 + 5.65) 1 + 7.4 = 21.1μs
K
20 1
10 2
5 4
2.5 8
Table 1.5-1 motionCAT communication times
CT = 7.7K
ST = (B0.6 + 3.25) K
JT = (B0.6 + 5.65) K
JT = 5.05K
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