Comtrol Modbus Server - Manual (Page 5)

DeviceMaster Modbus Server User Guide: 2000535 Rev. C Modbus Server Application Overview - 5
Modbus Server Application Overview
This section defines the software functionality for the Modbus Server application
and provides an overview of other Comtrol Modbus solutions (
Page 9 ).
The Modbus Server application was designed to provide enhanced connectivity for
OPC servers and applications that require Modbus/RTU communications. While
standard gateways provide connectivity for only one application per serial port,
Modbus Server provides connectivity for up to six applications per serial port.
Modbus Server was designed to greatly enhance system maintenance capabilities.
Included are comprehensive device and port specific diagnostic web pages that
display status, message response timing, timeout, and other error counts, and
overall message statistics. A serial log is also included to provide message level
diagnosis.
Recommended Chassis
The following table lists the recommended DeviceMaster UP chassis based on
Modbus/RTU message throughput.
Note: These estimates are based on a Modbus/RTU request and/or response
message size of 20 bytes. Actual throughput will vary depending on message
size and system requirements.
Throughput 1-Port 2-Ports 4-Ports
Very High - Message rate of up to one message every
50 ms per port (20 messages per port per second)
X X
High - Message rate of up to one message every 100
ms per port (10 messages per port per second)
X X X
Medium - Message rate of up to one message every
200 ms per port (5 messages per port per second)
X X X
Low - Message rate of up to one message every 500 ms
per port (2 messages per port per second)
X X X
Very Low - Message rate of up to one message every
second per port (1 message per port per second)
X X X
Latency
Transmit (From application to device) 2-10 ms (*)
Receive (From device to application 2-10 ms (*)
(*) = Based on one Ethernet TCP/IP connection per serial port running in a
normal uncongested system. The maximum overall latency will increase as the
number of Ethernet TCP/IP connections increase.