Ethernet Global Data Sweep Impact; Exchange Overhead; Byte Transfer Time - GE VersaMax PLC User Manual

Ethernet Global Data Sweep Impact

314 GFK-1503E
For public disclosure
Depending on the relationship between the CPU sweep time and Ethernet Global Data
(EGD) exchange's period, the exchange data may be transferred every sweep or
periodically after some number of sweeps. Therefore, the sweep impact will vary based
on the number of exchanges that are scheduled to be transferred during the sweep.
However, at some point during the operation of the PLC, all of the exchanges will be
scheduled to transfer data during the same sweep. Therefore, all exchanges must be
considered when computing the worst case sweep impact.
The Ethernet Global Data (EGD) sweep impact has two parts, Consumption Scan and
Production Scan:
EGD Sweep Impact = Consumption Scan Time + Production Scan Time
Where the Consumption and Production Scans consist of two parts, exchange overhead
and byte transfer time:
Scan Time = Exchange Overhead + Byte Transfer Time

Exchange Overhead

Exchange overhead includes the setup time for each exchange that will be transferred
during the sweep. This overhead varies depending on whether the exchange is consumed
or produced and if the time-stamp for the exchange originates from the PLC itself or from
a remote Network Time Protocol (NTP) server. When computing the sweep impact,
include overhead time for each exchange.
The NTP time synchronization feature is supported in IC200CPUE05-HK and previous
versions only.
Exchange Overhead †
†
Times are in microseconds.
††
Represents overhead if the exchange is time-stamped with the PLC clock
instead of a remote NTP server.

Byte Transfer Time

This is the time required to transfer data between the PLC CPU module and the Ethernet
module. The byte transfer time is slightly greater if the PLC memory being written to
could contain overrides due to additional overhead. The times shown in the following
table represent the time to transfer one data byte.
Byte Transfer Time †
† Times are in microseconds.
†† Represents transfer time if memory type supports overrides.
Consumed Exchange
80
Consumed Exchange
1 (3.6 †† )
Produced Exchange
110 (304 †† )
Produced Exchange
1
VersaMax PLC User Manual