thermoprozess MIKROTHERM 825 User Manual

MIKROTHERM® 825

MT825-A,

Communications

MT825A/C 11/09 Rev.3/Soft.4

THERMOPROZESS s.r.o.

Riegrova 2668/6c

370 01 České Budějovice

tel.: [phone]
fax : [phone]

e-mail: [e-mail]

internet : www.thermoprozess.cz

THERMOPROZESS

Communications

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1 Scope of communications

Communication line enhances usability of the controller from autonomous controller to the
one which performs the tasks in a system. Basic feasibilities are described in the 5 following
articles:

• Reading data from the controller, Prot = Mod. Enables to acquire data (SP values,

process values, ..) for PC, their visual data processing and storing. The form for showing
and presenting depends on the features of the visual program used.

• Configuration of controller, Prot = Mod. In graphic environment of PC you can

easily configure and set parameters that are transferred to PC by one command. The
configuration via PC can be used for example for more sophisticated setting of controllers
or for setting of production line by the technology procedures stored in PC.

• The controllers configured in system Master – Slave, Prot = SGnL. The controller

MT825A - MASTER retransmits set point value and the SLAVE - controllers (MT600)
receive this value and process it. In comparison with analog retransmit the MASTER­SLAVE system has the advantage in galvanic isolation of controllers and the precision of
transferring of STP value in 1 decimal point.

• Cascade controlling, Prot = SGnL. Used in process with long lag times between the

energy source and process measured value.

• Printing protocols of measurement, Prot = Prnt. Time, process and set point values

are shown on a printed copy, the format is illustrated below.

************************

DATE: 20.08.1999
************************

time: sp: c:

15:47 852 850
15:57 860 859
16:07 868 868
16:17 876 877

16:27 884 884

16:37 892 892

16:47 900 901
16:57 900 900
17:07 oFF 889
17:17 oFF 852

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2 Communication interfaces

The controllers can be equipped with communication interface RS 232 or EIA 485.
The baudrate of the communication is permanently set at 9600 Bd, the data bits is 8,
no parity, 1 stopbit.

2.1 Interface RS 232

The interface RS 232 is intended for the link of 1 PC with 1 controller. Maximum network
length can be 12 meters. The wiring of standard connectors DB-9 and DB-25 on the side of
PC is illustrated in the following picture.

2.2 Interface EIA 485

The interface EIA 485 is suitable for industrial environment. The local network with this
interface can link as many as 32 controllers with PC up to the distance 1200 meters. When
repeaters are used more controllers can be linked at longer distance. In basic wiring there
must be an appropriate converter or PC card for transferring of interface RS 232 to EIA 485 at
the side of PC.
If controllers work in the environment with low interference, the communication line can be
carried out with twisted pair cable. The simplest wiring of communication line illustrates the
following picture.

RS 232

EIA 485

Side of controller

Side of PC

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3 Protocol MODBUS

The communication protocol MODBUS is intended for creating networks of type „Master –
Slave“, when „Master“ is PC, „Slave“ are always controllers. Its characteristic is simple, but
reliable structure with these features:

• Defined length of transmitted commands.

• Identification of the terminal equipment with the address (for MT825 address 1 to 250).

• The back confirmation of each command.

• The report is secured with CRC code.

• The transfer of error reports.

3.1 General structure of protocol

Address of

controller

Command

Address of register and/or data CRC

1 byte 1 byte n bytes 2 bytes

The commands for MT825:

• Read – 03H or 04H

• Write to 1 register – 06H

• Back inquiry – 08H

3.2 Operation - read

This operation enables reading as many as 32 registers in a row one after another. If register is
not defined the controller returns the value – 32000, if the register is not active
the controller returns the value –32001.

Command:

Address of

controller

03H Address of 1. read register Number of read registers CRC

1 byte 1 byte

2 bytes (1. byte higher) 2 bytes (1. byte higher) 2 bytes

Response:

Address of

controller

03H Number of

bytes

1. read register … The last read register CRC

1 byte 1 byte 1 byte 2 bytes (1. byte

higher)

2 bytes (1. byte higher) 2 bytes

Example: reading of register 100 (64H, set point value), controller
at the address 12 (0CH)

Command: 0C 03 00 64 00 01 C4 C8
Response: 0C 03 02 01 C8 95 83

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3.3 Operation - write (06H)

This operation enables writing a value to 1 register of controller:

Command:

Address of

controller

06H Address of register Data CRC

1 byte 1 byte 2 bytes (1. byte higher) 2 bytes (1. byte higher) 2 bytes

Response if the command is performed (is identical with the command):

Address of

controller

06H Address of register Data CRC

1 byte 1 byte 2 bytes (1. byte higher) 2 bytes (1. byte higher) 2 bytes

Example: writing to register 100 (64H, set point value), controller at the address
12 (0CH)

Command: 0C 06 00 64 01 C8 C9 0E
Response: 0C 06 00 64 01 C8 C9 0E

Response, error report:

Address of

controller

Command +

80H

Error reports CRC

1 byte 1 byte 1 byte 2 bytes

Error reports:

• 01 – error of command entered, error in CRC.

• 02 – register does not exist or is intended only for reading.

• 03 – data are beyond the limits.

• 04 – writing to register failed (e.g. error of hardware, too high interference …)

Example: error of the register entered

Command: 0C 01 00 64 04 20 7F D0
Response: 0C 81 01 10 53

Example: error, the register does not exist

Command: 0C 06 00 69 04 20 5B D3
Response: 0C 86 02 52 62

Example: error, data beyond the limits

Command: 0C 06 00 64 4E 20 FD 70
Response: 0C 86 03 93 A2

3.4 Operation - back inquiry:

This operation is only intended for the detection of the controller at the relevant address.

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Command:

Address of

controller

08H Data CRC

1 byte 1 byte 4 bytes 2 bytes

Response:

Address of

controller

08H Data CRC

1 byte 1 byte 4 bytes 2 bytes

Example: back inquiry, controller at the address 12 (0CH)

Command: 0C 08 0A 14 1E 28 AB 74
Response: 0C 08 0A 14 1E 28 AB 74

3.5 Timing of communication line

If there is more than 1 controller on the line (only line EIA 485) it is necessary to observe the
timing shown in the following picture.
The time interval (pause between ending of receiving and transmitting of another command)
must be more or equal to 50ms. In opposite case the data collision might appear.

time

Transmitting
command

Receiving
response

Transmitting of

another
command

Receiving
response

Interval >= 50 ms