Reading n words, Writing 1 word | Siemens RS-485 specification

Reading n words

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

Data query

Slave address

Function 0x03

Address of the

Number of

Checksum

or 0x04

first word

words

CRC16

(max. 12)

1 byte

2 bytes

Slave address

Function 0x03

Number of

Word value(s)

Checksum

or 0x04

bytes read

CRC16

1 byte

x byte(s)

2 bytes

Example

Reading the 2 setpoints of the controller

Word address = 0x0008 (setpoint SP1)

Data query:

CRC16

Reply:

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.

Instruction

Slave address

Function 0x06

Word address

Word value

Checksum

CRC16

1 byte

2 bytes

Slave address

Function 0x06

Word address

Word value

Checksum

CRC16

1 byte

2 bytes

Example

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

Word address = 0x000C

Instruction: (write the first part of the value)

CRC16

Reply (like instruction):

CRC16

Instruction: (write the second part of the value)

CRC16

Reply (like instruction):

CRC16

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Siemens Building Technologies	CC1A7865.1en
HVAC Products	31.10.2002