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Siemens RS-485 User Manual

Siemens RS-485
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CC1A7865.1en
31.10.2002
Siemens Building Technologies
HVAC Products
7
865.1
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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Siemens RS-485 Specifications

General IconGeneral
Interface TypeRS-485
Data RateUp to 10 Mbps
Maximum Cable Length1200 meters (at 100 kbps)
Number of Devices/NodesUp to 32 devices (without repeaters)
TopologyBus
Differential Voltage1.5V to 5V
Common Mode Voltage-7V to +12V
Humidity5% to 95% (non-condensing)
Communication ProtocolModbus, Profibus, others

Summary

Interface RS-485

Master-slave principle

Communication between PC (master) and device (slave) via MOD bus protocol.

Transmission Mode and Data Format

Data Format Structure

Describes the structure of the transmitted byte, including data word, parity, and stop bits.

Device Addressing

Slaves' device addresses range from 1 to 99. Address 0 is reserved for broadcast.

Communication Sequence Timing

Character Transmission Time Calculation

Defines character transmission time calculation based on Baud rate and data format.

Example Waiting Time Calculation

Illustrates waiting time calculation for data query/reply based on baud rate and data format.

Data Query Sequence and Timing

Time Sequence Overview

Illustrates the timing of a data query, including master and slave responses and delays.

Communication Restrictions During Slave Operations

Master must not query during slave's internal handling or response time to avoid data issues.

Data Block Structure and Fault Handling

Data Block Structure

Defines the standard structure of all data blocks: Slave address, Function code, Data field, and Checksum.

Fault Handling and Error Codes

Lists 3 error codes and describes the reply format in case of a fault.

Special Cases for Slave Reply

Lists conditions under which the slave does not reply, such as incorrect checksum.

Checksum (CRC16) for Error Detection

CRC16 Calculation Method

Explains the CRC16 calculation method used to detect transmission errors.

CRC16 Calculation Example

Shows examples of CRC16 calculation for data queries and replies.

Data Read and Write Functions

Reading n Words

Defines the data block structure for reading multiple words from a specific address.

Writing 1 Word

Defines the data block structure for writing a single word, including instruction and reply.

Writing Multiple Words and Data Types

Writing n Words

Defines the data block structure for writing multiple words, including instruction and reply.

Data Types: Char and Float

Explains transmission of character ('char') and floating-point ('float') data types.

Parameter Address Tables

Process Data Addresses

Lists addresses, data types, access, and parameters for process data.

Parameter and Configuration Levels

Lists addresses, data types, access, and parameters for parameter and configuration settings.

Device Data and Remote Operation

Remote Operation Parameters

Lists parameters related to remote operation modes, including activation and setpoint control.

Device State and Identification

Outputs and States Bit Assignments

Describes bit assignments for outputs and states in device status words (0x0200).

Binary Signal and Hardware ID

Describes bit assignments for binary signals and hardware identification (0x0201).

Description of Operating Modes

General Operating Modes

Introduces operating modes (LOCAL, REMOTE SETPOINT, FULLY REMOTE) and parameter <<RemoteStatus>>.

Remote Operation RAM Parameters

Lists parameters relevant to remote operation that are stored in RAM.

LOCAL Operating Mode

REMOTE SETPOINT Operating Mode

FULLY REMOTE Operating Mode

Modulating and Floating Step Control Strategies

Setpoint-Dependent Value Supervision

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