Vega VEGACOM 557 Modbus protocol Bedienungsanleitung PDF herunterladen (Seite 42)

42 VEGACOM 557 Modbus

Data transmission with Modbus RTU

Error messages in RTU mode

Errors in the telegram of function code 04 (Read Input Register) are commented by an error

message (Exception Response). The most significant bit of the function code is set to 1 (cor-

responds to function code + 80H). In the byte Exception Code, the error is named in coded

form (see error overview).

Error overview:

Exception Code Meaning

1 unpermitted function

2 unpermitted start register

3 unpermitted number of registers

Example for error message:

A DCS value should be collected from a VEGAMET 513. VEGACOM 557 operates in mode

"Sort measured values acc. to VEGAMET addresses“. The Slave-address of VEGACOM 557

is set to 1.

In the enquiry telegram, 240 was inadvertently enquired as start register. The highest possible

Start

Slave

ad-

dress

Func-

tion

code

Ex-

ception

code

Error

Check

End

No. of

Bytes

Value

range

Meaning

Structure of the answer VEGACOM 557 to Modbus-Master

TU answer telegram (function code 04) to faulty enquiry

3 ... 4 1 1 1

2 3 ... 4

Closed level

1 .. 247 0x84

1 ..

CRC Closed level

0x01 0x84 0x02 0xXX0xXX

Exception Code = 2

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 67 68

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