Minebea Sartorius Intec Maxxis 4 PR 5500, Instrument Manual, Page: 368 / 407

ModBus Protocol PR 5500 Instrument Manual
EN-422 Sartorius
7.3 ModBus-TCP/UDP
Connection is via the network interface.
The telegram consists of six blocks:
Trans
16
Proto
16
Size
16
Addr
8
Func
8
<data>
Legend
Trans
16
Sequential transaction number. This number is used by the device so that the reply can be
assigned to the query.
Proto
16
Reserved for future upgrades, always 0 here.
Size
16
Number of following bytes
Addr
8
Normally, the device address is not used with ModBus-TCP/UDP.
It is used if ModBus-TCP/UDP is connected behind a ModBusRTU gateway.
The device ignores this parameter for ModBus-TCP/-UDP.
Func
8
Function code (see Chapter 7.4)
<data> Additional data (see Chapter 7.4)
Telegrams can be exchanged using TCP or UPD via Port 502. Normally, this is a fixed setting in the ModBus-TCP
master.
For UDP, the reply time is typically 4 ms and a max. of 8 ms. When network traffic is heavy, failed telegram
transmissions must be expected. Suitable measures must be taken in the Modbus-UDP master to force a
repeated transmission in the event of telegram loss.
With TCP, the typical response time is approx. 10 ms. With heavy network traffic, transmission can be delayed
(max. 120 seconds for extreme network loads or for long transmission distances such as via the Internet).
However, no telegrams are normally lost.
Comparison
ModBus-TCP ModBus-UDP
Reliable transmission: Unreliable transmission:
As long as the line is not interrupted, no telegram is
lost. With heavy network traffic or transmission over long
distances, telegram loss must be expected.
Low speed: High speed:
With transmission problems, transmission can be
delayed considerably. The reply is transmitted quickly, or not at all.
Suitable for: Suitable for:
- Parameter transmission - Transmission of dynamic values
- Result logging - Visualization
- Non-time-critical process control - Time-critical process control (requiring timeout
handling)