Azbil AUR355 - Page 14

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Chapter 4. Communication
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Response start conditions
The slave station sends a response message only if all the message components
(device address, subaddress, and checksum) in the data link layer are correct. If
even one of these is incorrect, no response message is sent, and the slave device
stands by to receive STX.
If the message exceeds the allowed length (160 bytes), no response message is sent,
and the slave station waits for a new message.
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List of data link layer data definitions
The following table describes the data in the data link layer.
Data name Character code Bytes Meaning
STX 02H 1 Start of message
Device address Hexadecimal 2 The device to communicate with
Subaddress Hexadecimal 2 Always 00
Device distinction code “X” (58H) or “x” (78H) 1 Type of device
ETX 03H 1 End of application layer
Checksum 2 hexadecimal digits
from 00H to FFH
2 Checksum of message
CR 0DH 1 End of message marker (part 1)
LF 0AH 1 End of message marker (part 2)
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Description of data
z STX (02H)
When STX is received, this device interprets it as the start of a transmitted message.
It follows that, no matter what has been received previously, upon receiving STX the
device begins processing a new message. The purpose of this is to enable recovery
of the device’s responsiveness when the next message (for example, a RETRY
message) comes from the master station in the event that electromagnetic noise, for
example, caused an error in the command message.
z Device address
The slave station only creates response messages to messages that contain its device
address. Device addresses in the messages are expressed as two-digit hexadecimal
characters.
The setting range for the device address is 1–32.
When the slave station responds, it adds its device address to the response message.
z Subaddress
The AUR355 does not use subaddresses. For this reason, set the subaddress to “00”
(30H 30H). When the slave station responds, it adds the subaddress to the response
message.
z Device distinction code
Either X (58H) or x (78H) can be used. This code is determined for each device
series, and other characters cannot be used. The slave station adds the same device