Lenze E94P PositionServo Modbus Manuel d'utilisateur télécharger pdf (Page 27)

27 P94MOD01C

Protocol Implementation

5.7 Exception Responses

If an invalid message is received, the drive will respond with a Modbus Exception as per the “Modbus application

Protocol speciﬁcation V1.1”, i.e. the exception function code = the request function code + 0x80 (an exception

code is provided to indicate the reason of the error).

Table 9: Exception Codes

Code V1.1 Speciﬁcation Description

0x01 Illegal Function function not supported by PositionServo

0x02 Illegal data address requested address is not a valid register address

0x03 Illegal Data Value set value not valid for speciﬁc variable

5.8 Modbus Message Frame

The Modbus protocol deﬁnes a simple protocol data unit (PDU) independent of the underlying communication

layers. There are additional application data unit (ADU) ﬁelds introduced by the network layer.

ADU for Modbus RTU

PDU

Address Function Code Data Error

Figure 18: Modbus RTU Frame EIA-485

ADU for Modbus TCP/IP

PDU

Length

Unit Identifier Function Code

Data

Transaction

Protocol Identifier

MBAP

Figure 19: Modbus TCP/IP Request/Response

5.8.1 PDU Function Code

• Size = 1 byte

• The function code indicates what kind of action to perform.

• The function code (depending upon the function) is normally followed by a data ﬁeld that contains request

and response parameters.

5.8.2 PDU Data

The data ﬁeld of messages sent from a master/client to slave/server device contains additional information that

the slave/server uses to take the action deﬁned by the function code. This can include items like discrete and

The data ﬁeld may be nonexistent (of zero length) in certain kinds of requests. In this case the slave/server does

not require any additional information. The function code alone speciﬁes the action.

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Lenze E94P PositionServo Modbus Manuel d'utilisateur Page 27