User manual

Modbus Commands

2-16

SIMATIC TI505/TI500 MODNIM User Manual

Modbus Function Descriptions (continued)

Code

06 allows the contents of a holding register to be changed. Addressing

is sequential up to the maximum memory size for a particular PLC. This

function is limited to integer values contained in V

-memory

. The MODNIM

will also direct any broadcast address (00) to all attached secondaries.

[This command is comparable to a TIW

Y I request using Primitive 30 and

-type 01 (V

ariable memory)].

Because

of differences in memory mapping between Modbus PLCs

and SIMA

TIC TI PLCs, you should be quite certain of the effects of

the broadcast command before issuing it.

Example:

Request: 07 06 0064 0220 XXXX

Checksum (XXXX)

Data value (0220)

Function code (06)

Slave address (07)

Figure 2-16 Write

a Single Register Example — Request

This request to secondary 7 is asking for the value of holding register 0064

(100 decimal) to be changed to 0220 (544 decimal).

Response: 07 06 0064 0220 XXXX

Checksum (XXXX)

Data value (0220)

Function code (06)

Slave address (07)

Figure 2-17 Write

a Single Register Example — Response

The response to Function Code 06 is to return the request as received. In

the case of a broadcast request, there is no response.

Code 06 — W

rite a

Single Register

WARNING