User manual

D. MODBUS Interface

D.1. General information

For remote control and monitoring of devices the MODBUS interface in each CS121 M can

read out measurement values, events, status and other information in a master-slave protocol.

Note: Please note that not all UPS models support all or specific measurement

values (e.g. battery low).

D.2. Available Modbus Function Codes

Implemented MODBUS functions in the CS121 M units:

01H Read Coils

02H Read Discrete Inputs

03H Read Holding Registers

04H Read Input Registers

05H Write Single Coil

Which functions are supported depends on the connected UPS. For standard UPS only

functions 03H and 04H are available. In this case the CS121 M makes no difference between

function 03H and 04H. The baud rate is adjustable up to 115200 Baud.

Note: Please note that the MODBUS adapter client allows a timeout of 40ms at

9600 baud for one value.

D.3. Exception Codes

Except for broadcast messages, when a master device sends a query to a slave device it

expects a normal response. One of four possible events can occur from the master's query:

If the slave device receives the query without a communication error, and can handle the query

normally, it returns a normal response.

If the slave does not receive the query due to a communication error, no response is returned.

The master program will eventually process a timeout condition for the query.

If the slave receives the query, but detects a communication error parity, LRC, or CRC, no

response is returned. The master program will eventually process a timeout condition for the

query.

If the slave receives the query without a communication error, but cannot handle it (for

example, if the request is to read a non existent register the slave will return an exception

response informing the master of the nature of the error.

Available Exception codes:

Code Meaning

01H Illegal Function:

The command received in the query is not defined.

02H Illegal Address:

The address received in the query is not defined for the slave.

04H Slave Device Failure:

Internal slave device error.

D.4. MODBUS Modes in the CS121 M (ASCII and RTU)

MODBUS Command

The following tables contain the general command descriptions and examples with ASCII and

RTU framing.

Read Words (Functions 03h and 04h)