Siemens RS-485 Manuale utente

CC1A7865.1en

31.10.2002

Siemens Building Technologies

HVAC Products

7865.1

Interface RS-485 RWF40...

The RS-485 interface is used for integrating RWF40… controllers into data networks

via MOD bus protocol.

Application examples:

- Process visualization

- Plant control

- Reporting

Master-slave principle

Communication between a PC (master) and a device (slave) via MOD bus is based on

the master-slave principle in the form of data query / instruction – reply.

A master computer controls the exchange of data and can address up to 99 controllers

via device addresses (slaves).

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Transmission mode (RTU)

The transmission mode used is the RTU (remote terminal unit) mode. Data are trans-

mitted in binary format (hexadecimal) with 8 bits.

The LSB (least significant bit) is transmitted first.

ASCII mode is not supported.

The data format describes the structure of the transmitted byte.

Data word Parity bit Stop bit ½ bit Number of bits

8 bit Not 1 9

Device address

The slaves’ device addresses can be selected between 1 and 99.

Device address 0 is reserved.

+A maximum of 31 slaves can be addressed via the RS-422 / RS-485 interface.

There are 2 choices of data exchange:

Query Data query / instructions delivered by the master to a slave via the re-

spective device address.

The addressed slave responds.

Broadcast Master instructions to all slaves via device address 0.

The addressed slaves do not respond.

A data query with device address 0 does not make sense.

A certain setpoint can be transmitted to all slaves, for example.

In that case, correct adoption of the value by the slaves should be

checked by subsequent setpoint readout.

Data format

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Communication sequence

Both the start and end of a data block are characterized by transmission pauses. The

maximum period of time that may elapse between 2 successive characters is 3 times

the period of time required for the transmission of one character.

The character transmission time (period of time required for the transmission of 1 char-

acter) is dependent on the Baud rate and the type of data format.

Using a data format of 8 data bits, no parity bit and 1 stop bit, the character transmis-

sion time is calculated as follows:

Character transmission time [ms] = 1000 * 9 bits / Baud rate

Data query by the master

Transmission time = n characters * 1000 * x bits / Baud rate

Identification of end of data query

3 characters * 1000 * x bits / Baud rate

Handling of data query by the slave (£250 ms)

Reply by the slave

Transmission time = n characters * 1000 * x bits / Baud rate

Identification of end of reply

3 characters * 1000 * x bits / Baud rate

Identification of the data query or end of the reply with a data format of 10 / 9 bits.

Waiting time = 3 characters * 1000 * x bits / Baud rate

Baud rate Data format [bits] Waiting time [ms]

9.600 9 2.813

19.200 9 1.406

Process

Example

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Data query sequence

The time sequence of a data query looks as follows:

Master

Slave

Data query

t0t1t0t2

7865z12e/1102

t0 Identification of end = 3 characters

(time is dependent on the Baud rate)

t1 This time is dependent on internal handling.

The maximum handling time is 250 ms

t2 This is the time required by the device to switch from the transmitting mode back

to the receiving mode.

This time must be observed by the master before it makes a new data query. It

must always be maintained, even if the new data query is sent to some other

device.

t2 ³20 ms

Communication during the slave’s internal handling time

The master is not allowed to make any data queries during the slave’s internal handling

time.

Data queries made during that period of time will be ignored by the slave.

Communication during the slave’s response time

The master is not allowed to make any data queries during the slave’s response time.

Data queries made during that period of time cause all data currently on the bus to

become obsolete.

Time sequence

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Structure of the data blocks

All data blocks use the same structure:

Slave address Function code Data field Checksum CRC16

1 byte 1 byte x byte 2 bytes

Every data block contains 4 fields:

Slave address Device address of a certain slave

Function code Function selection (reading or writing words)

Data field Contains the following information:

- Word address

- Number of words

- Word value

Checksum Identification of transmission errors

Fault handling

3 different error codes are used:

1 Invalid function

2 Invalid parameter address

8 Write access to parameter rejected

Slave address Function

XX OR 80 h

Error code Checksum CRC16

1 byte 1 byte 1 byte 2 bytes

The function code is OR linked with 0 x 80, that is, the MSB (most significant bit) will be

set to 1.

Data query:

01 02 00 70 00 04 CRC16

Reply:

01 82 01 CRC16

In the following cases, the slave does not reply:

- The checksum (CRC16) is wrong

- The instruction given by the master is incomplete or overdefined

- The number of words or bits to be read is zero

Data structure

Error codes

Reply in the event

of fault

Example

Special cases

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Checksum (CRC16)

The checksum (CRC16) is used to detect transmission errors.

If the evaluation reveals an error, the relevant device will not respond.

CRC = 0xFFF

CRC = CRC XOR ByteOfMessage

For (1 to 8)

CRC = SHR (CRC)

if (flag to the right = 1)

then

CRC = CRC XOR

0xA001

else

while (not all ByteOfMessage edited)

+The low byte of the checksum will be transmitted first.

Data query:

Reading 2 words from address 6 (CRC16 = 0x24A0)

0B 03 00 06 00 02 A0 24

CRC16

Reply:

(CRC16 = 0x6105)

0B 03 04 00 00 42 C8 61 05

Word 1 Word 2 CRC16

The following functions for the device will be available:

Function number Function

0x03 / 0x04 Reading n words (n £12)

0x06 Writing 1 word

0x10 Writing n words (n £2)

Calculation

Example

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Reading n words

This function is used to read n words from a certain address.

Slave address Function 0x03

or 0x04

Address of the

first word

Number of

words

(max. 12)

Checksum

CRC16

1 byte 1 byte 2 bytes 2 bytes 2 bytes

Slave address Function 0x03

or 0x04

Number of

bytes read

Word value(s) Checksum

CRC16

1 byte 1 byte 1 byte x byte(s) 2 bytes

Reading the 2 setpoints of the controller

Word address = 0x0008 (setpoint SP1)

Data query:

0B 03 00 08 00 04 CRC16

Reply:

0B 03 08 0000 42C8 0000 4316 CRC16

Setpoint 1 (100) Setpoint 2 (150)

Writing 1 word

With the “Wordwriting” function, the data blocks for instruction and reply are identical.

Slave address Function 0x06 Word address Word value Checksum

CRC16

1 byte 1 byte 2 bytes 2 bytes 2 bytes

Slave address Function 0x06 Word address Word value Checksum

CRC16

1 byte 1 byte 2 bytes 2 bytes 2 bytes

Write limit value limit comparator 1 (AL1) (= 275)

Word address = 0x000C

Instruction: (write the first part of the value)

0B 06 00 0C 80 00 CRC16

Reply (like instruction):

0B 06 00 0C 80 00 CRC16

Instruction: (write the second part of the value)

0B 06 00 0D 43 89 CRC16

Reply (like instruction):

0B 06 00 0D 43 89 CRC16

Data query

Example

Instruction

Example

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Writing n words

Slave

address

Function

0x10

Address

of first

word

Number of

words

Number of

bytes

(max. 2)

Word

value(s)

Check-

sum

CRC16

1 byte 1 byte 2 bytes 2 bytes 1 byte x byte(s) 2 bytes

Slave address Function 0x10 Address of

first word

Number of

words

Checksum

CRC16

1 byte 1 byte 2 bytes 2 bytes 2 bytes

Write switch-on threshold (Hys1 = -10)

Word address = 0x0018

Instruction:

0B 10 00 18 00 02 04 00 00 C1 20 CRC16

Reply:

0B 10 00 18 00 02 CRC16

The high byte must be transmitted first.

Example: Configuration code C111: “9030“

MOD bus: 0B10 0024 00 02 04 0903

The following explanations apply under the condition that the master works with the

IEEE-754 format. Before transmitting a value, the bytes must be exchanged in a way

that the order corresponds to the presentation for the MOD bus (see illustration below).

M-23 bit normalized mantissa

E-exponent (complement to base 2)

S-Sign-bit; 1 = negative, 0 = positive

MOD-Bus

Master

Read

Write

MMMMMMMM MMMMMMMM SEEEEEEE EMMMMMMM

EMMMMMMM

SEEEEEEE MMMMMMMM MMMMMMMM

(IEEE 754)

7865z13e/1102

Example:

Transmission of decimal value “550“:

MOD bus: 0x80, 0x00, 0x44, 0x09

Following is a description of all process values (variables) with their addresses, data

type and type of access.

Where:

R / O Read only access

R / W Read and write access

float Float value (4 bytes / 2 words)

word Integer (2 bytes / 1 word)

The process values are subdivided into logic areas.

Instruction

Example

Data type “char“

Data type “float“

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Address tables

Address Data

type

Access Parameter Value range Default

value

0x0000 float R / O Actual value E1

0x0002 float R / O Actual value E2

0x0004 float R / O Actual value E3

0x0006 float R / W Current setpoint

0x0008 float R / W SP1 First setpoint SPL...SPH 0

0x000A float R / W SP2 (=dSP) Second setpoint SPL...SPH 0

Address Data

type

Access Parameter Value range Default

value

0x000C float R / W AL Limit value limit comparator -1999...9999 0

0x000E float R / W Pb1 Proportional band 0.1...9999 10

0x0010 float R / W dt Derivative action time 0...9999 80

0x0012 float R / W rt Integral action time 0...9999 350

0x0014 float R / W db Dead band (neutral zone) 0.0...100.0 1

0x0016 float R / W tt Actuator running time 10...3000 15

0x0018 float R / W Hys1 Switch-on threshold 0...-199.9 -5

0x001A float R / W Hys2 Switch-off threshold, bottom 0...Hys3 3

0x001C float R / W Hys3 Switch-off threshold, top 0.0...999.9 5

0x001E float R / W q Reaction threshold 0.0...999.9 0

0x0020 float R / W H Heating curve slope 0.0...4.0 1.0

0x0022 float R / W P Parallel displacement

room temperature

-90...90 0

Address Data

type

Access Parameter Value range Default

value

0x0024 char [4] R / W C111 9030

0x0026 char [4] R / W C112 0010

0x0028 char [4] R / W C113 0110

0x002A char [4] R / W C000 0000

0x002C float R / W SCL Normalization start value: Input 1 -1999...9999 0

0x002E float R / W SCH Normalization end value: Input 1 -1999...9999 100

0x0030 float R / W SCL2 Normalization start value: Input 2 -1999...9999 0

0x0032 float R / W SCH2 Normalization end value: Input 2 -1999...9999 100

0x0034 float R / W SPL Start value setpoint limitation -1999...9999 0

0x0036 float R / W SPH End value setpoint limitation -1999...9999 100

0x0038 float R / W OFF1 Offset input 1 -1999...9999 0

0x003A float R / W OFF2 Offset input 2 -1999...9999 0

0x003C float R / W OFF3 Offset input 3 -1999...9999 0

0x003E float R / W HYST Hysteresis of limit comparator 0...9999 1

0x0040 float R / W df1 Filter time constant input 1 0.0...100.0 1.0

0x0042 float R / W dF3 Filter time constant input 3 0...1440 1278

0x0044 float R / W dtt Bus detection timer 0...7200 * 30

0x0046 float R / O oLLo Start value actual value limit -1999...9999 -1999

0x0048 float R / O oLHi End value actual value limit -1999...9999 9999

* Timer = 0 means switched off

This parameter can only be changed via the management system

Process data

Parameter level

Configuration level

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Address Data

type

Access Parameter Value range Default

value

0x0300 word [13] R / O Device data

0x0300 char SWVersion [11+1] Software version

0x0306 char VDNNr [13+1] VdN number

Address Data

type

Access Parameter Value range Default

value

0x0400 float R / O TEMP Actual value E3 (unfiltered)

0x0500 word R / W REM Activation remote operation 0...2 * 0

0x0501 word R / W ROFF Controller OFF in REMOTE

SETPOINT

0...1 ** 0

0x0502 float R / W RHYS1 Switch-on threshold REMOTE 0...-1999 HYS1

0x0504 float R / W RHYS2 Switch-off threshold bottom

REMOTE

0...RHYS3 HYS2

0x0506 float R / W RHYS3 Switch-off threshold top REMOTE 0...9999 HYS3

0x0508 float R / W SPR Setpoint REMOTE SPL...SPH SP1

0x050A word R / W RK1 Burner control remote operation 0...1 0

0x050B word R / W RK2 Relay K2 remote operation 0...1 0

0x050C word R / W RK3 Relay K3 remote operation 0...1 0

0x050D word R / W RK6 Relay LK remote operation 0...1 0

0x050E word R / W RSTEP Step control remote operation -100...100 0

0x050F float R / W RY Positioning output remote

operation

0...100 0

* 0 = local ** 1 = controller OFF

1 = remote setpoint

2 = fully remote

Device data

Remote operation

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