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4-4SectionApplication Procedure
47
that is included in the frame makes it possible to check for data errors in the
frame.
FCS
↵
01RR0@00142
Text
Node No.
Header code
FCS calculation range
Terminator
@ 40 0100 0000
EOR
1 31 0011 0001
EOR
0 30 0011 0000
EOR
R 52 0101 0010
1 31 0011 0001
0100 0010
↓↓Converted to hexadecimal.
4 2 Handled as ASCII characters.
ASCII code
Calculation
result
The right to send a frame is called the “transmission right.” The Unit that has the
transmission right is the one that can send a frame at any given time. The trans-
mission right is traded back and forth between the host computer and the PC
each time a frame is transmitted. An example sequence for multiframe commu-
nications between the host computer and PC is described below. Multiframe
communications are handled by exchanging delimiters and then using termina-
tors to indicate the last frame.
• The host computer sets a delimiter at the end of the first command frame and
transmits the frame.
• When the PC receives the delimiter, it returns the same delimiter to the host
computer.
• After receiving the delimiter from the PC, the host computer transmits the next
frame.
• Delimiters are used to send the rest of the frames.
• When the host computer sends the last command frame, it sets a terminator at
the end.
• When the PC receives a frame with a terminator, it sends the response.
• If there was more than one response frame, delimiters would be used here too.
Delimiter
Text
@ Unit No.
Header code
FCS
Delimiter
Frame 1 (command)
Text
FCS
Delimiter
Terminator
FCS
Text
End code
Header code
@ Unit No.
Frame 2 (command)
Frame (response)
Delimiter
Text
FCS
Terminator
Frame 3 (command)
Host
computer
PC
Communications
Sequence