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Modbus Commands

2-30

SIMATIC TI505/TI500 MODNIM User Manual

Modbus Function Descriptions (continued)

Code

1 returns a 2-byte status word and an associated 2-byte event

counter

. The status word is defined in the Modbus Protocol Reference

Specification as being 0 for no command in progress and FFFF if a previous

command is in progress. The status will always be 0 in the MODNIM.

The event counter is incremented for every successful message; it is not

incremented for exceptions or polls, or for this code or Code 12. This code

can be used to determine if a single command was successful when a

communication error occurred during the request or response.

The event counter will increment to the value FFFF (65535 decimal), then

begin again from zero.

Example:

Request: 15 0B XXXX

Checksum (XXXX)

Function code 1

1 (0B hex)

Slave address 21 (15 hex)

Figure 2-23 Get

Comms Event Counter Example — Request

In this example, secondary node 21 (15 hex) has been asked to return the

event counter and the associated status word.

Response: 15 0B 0000 0143 XXXX

Checksum (XXXX)

Number of events (0143)

Status word (0000)

Function code 1

1 (0B hex)

Slave address 21 (15 hex)

Figure 2-24 Get

Comms Event Counter Example — Response

The response shows that the status word is 0000 and that 323 (decimal)

events have occurred.

Code 11 — Get

Comms Event

Counter

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