Nor-Cal SDC15 Controller - Manual (Page 162)

● List of data link layer data definitions
The following list shows the definitions for data in the data link layer:
● Description of data items
• STX (02H)
When STX is received, the device judges this to be the start of the send message.
For this reason, the device returns to the initial state whatever reception state it
was in, and processing is started on the assumption that the STX, the first
character, has been received. The purpose of this is to enable recovery of the
device's response at the next correct message (e.g. RETRY message) from the
master station in the event that noise, for example, causes an error in the sent
message.
• Station address
Of the messages sent by the master station, the device creates response messages
only when station addresses are the same. Station addresses in messages are
expressed as two-digit hexadecimal characters.
The station address is set up by the station address setup (setup setting C65).
However, when the station address is set to 0 (30H 30H), the device creates no
response even if station addresses match.
The device returns the same station address as that received as the response
message.
• Sub-address
The SDC15 does not use the sub-address. For this reason, set "00" (30H 30H).
The device returns the same sub-address as that received as the response
message.
• Device ID code
The device sets X (58H) or x (78H) as the device ID code. This code is
determined for each device series, and other codes cannot be selected. The
device returns the same device ID code as that received as the response message.
X (58H) is used as the default, and x (78H) is used for judging the message as the
resend message.
• ETX
ETX indicates the end of the application layer.
• Checksum
This value is for checking whether or not some abnormality (e.g. noise) causes
the message content to change during communications.
The checksum is expressed as two hexadecimal characters.
7-4
Chapter 7. CPL COMMUNICATIONS FUNCTIONS
Data name Character code Number of Meaning of data
characters
STX 02H 1 Start of message
Station address 0 to 7FH are expressed as 2 Identification of device
hexadecimal character codes. to communicate with
Sub-address "00" (30H, 30H) 2 No function
Device ID code "X" (58H) or "x" (78H) 1 Device type
ETX ETX (03H) 1 End position of the
application layer
Checksum 00H to FFH are expressed as two- 2 Checksum of message
digit hexadecimal character codes.
CR 0DH 1 End of message (1)
LF 0AH 1 End of message (2)