Bedienungsanleitung Daikin EUWA water chillers (Seite 20 von 28) (Englisch)

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Installation and operation manual

EUWA(*)5~24KBZW1

Packaged air-cooled water chillers

4PW61653-1 – 07.2010

General information about the Modbus protocol

The Modicon Modbus protocol implemented in the address card

complies with the content of the following document:

Modicon Modbus Protocol

Reference Guide

June 1996, PI-MBUS-300 Rev. J

The Modbus protocol implemented is of the RTU (Remote Terminal

Unit) type based on character tranmission times. The conﬁguration

uses the multi-drop feature of RS485. The address sent within the

Modbus packet addresses the chiller unit.

Implemented RS485 communication settings for the Modbus

protocol

The RS485 communication settings are implemented as follows:

■ Baud-rate: 9600

■ Stop bit: 2

■ Parity: none

Implemented commands for the Modbus protocol

The implemented commands in the program are as listed:

Note that:

■ Due to the variety of chillers with installed address cards, no

distinction is made between input variables (with read-only

status) and output variables (with read/write status) so that the

knowledge of the database and its management depends on the

part present on the supervisory system.

■ Due to the general nature of the system, the address card

answers in the same way to various Modbus commands.

Data representation of the Modbus protocol

■ Digital

All digital data is coded by a single bit:

■ "0" for OFF

■ "1" for ON.

All digital variables are assigned to bits of consecutive registers,

each one having:

■ the lower-address variable assigned to the less signiﬁcant bit

■ the higher-address variable assigned to the most signiﬁcant

bit.

■ Analogue and integer data

An analogue and integer value is represented by a 16-bit WORD

contains the high order bits and the second byte contains the

low order bits.

■ The analogue variables are represented in tenths:

for example, the value 10.0 is transmitted as 0064h=100d

for example, the value –10.0 is transmitted as FF9Ch=–100d

■ The integer variables are transferred using the effective

value:

for example, the value 100 is transmitted as 0064h=100d

The address card operates on registers where one register must

be considered at 16-bit.

In case the BMS or supervisory system tries to write a value of a

parameter that is out of range, the writing will be ignored.

Implemented error code

Deﬁning the BMS setting

Activating the Modbus protocol

The Modbus protocol is activated by setting the h23 parameter to 1.

This is a user parameter, refer to "How to consult and modify the user

parameters" on page 15.

Deﬁning the unit’s serial address

To deﬁne each unit’s unique serial address required for

communication with the supervisionary system, set parameter h10.

This is a user parameter, refer to "How to consult and modify the user

parameters" on page 15.

Modbus command Meaning Notes

01 read coil status Read digital

variable(s)

obtains current status (ON/

OFF) of a group of logic coils

or discrete input

02 read input

status

Read digital

variable(s)

obtains current status (ON/

OFF) of a group of logic coils

or discrete input

03 read holding

registers

Read analogue

variable(s)

obtains current binary value

in one or more holding

registers

04 read input

registers

Read analogue

variable(s)

obtains current binary value

in one or more holding

registers

05 force single coil Write individual

digital variable(s)

forces single coil to ON or

OFF status

06 preset single

Write individual

analogue variable(s)

places a speciﬁc binary

value into a holding register

15 force multiple

coils

Write series of

digital variables

forces a series of

consecutive logic coils to be

deﬁned to ON or OFF status

16 preset multiple

registers

Write series of

analogue variables

places speciﬁc binary values

into a series of consecutive

holding registers

Code Modbus interpretation Condition

1 Illegal function Message is not supported or the

number of variables required is greater

than the allowed limit (length ≤20)

4PW61653-1_digital_EN.book Page 17 Thursday, August 26, 2010 1:49 PM

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