Ethernet Units Operation Manual

94
Sending Commands From a PC Section 5-3
SEND(090)
The transmission delay for the SEND(090) instruction can be calculated using
the following equation, which is illustrated in the following diagram.
Max. delay = Local node service cycle + local node service processing time
+ transmission processing time + reception processing time +
remote node service cycle + remote node service processing
time + CPU data set processing time (remote node)
CPU Bus Unit Service
Cycle
The CPU Bus Unit service cycle is a single PC cycle.
CPU Bus Unit Service
Processing Time
This is the time required to process CPU Bus Units and is approximately 1 ms
for Ethernet Units.
Transmission Processing
Time
Number of words transferred x 0.011 + 3 ms
Reception Processing
Time
Number of words transferred x 0.011 + 3 ms
CPU Data Set Processing
Time
Number of words transferred x 0.02 + 20 ms
Note 1. The actual operating environment can cause transmission delays larger
than those calculated with the methods given here. Among the causes of
longer delays are the following: traffic on the network, window sizes at net-
work nodes, traffic through the Ethernet Unit (e.g., socket servicing, FTP
server communications, etc.), and the system configuration.
2. The CPU data set processing time is the standard when the peripheral ser-
vice time is set in the CPU Unit System Setup to the default of 4%. As this
value is increased, the processing time is shortened.
Example Calculations The following example shows calculations for sending 256 words between two
PC nodes using SEND(090). The local node’s CPU cycle time is 10 ms, and
the remote node’s CPU cycle time is 5 ms. Calculations are shown in the fol-
lowing table.
Maximum transmission delay
SEND(090) executed
in user program
CPU Bus Unit service cycle (local node)
CPU Bus Unit service processing time (local node)
Transmission processing time
Reception processing time
CPU Bus Unit service cycle (remote node)
CPU Bus Unit service processing time (remote node)
CPU data set processing time (remote node)