Omron SYSMAC C200HS Operation Manual page 410

Command and Response Formats
Long Transmissions
Frame1 (command)
Unit no.
Header code
Host
Text
computer
FCS
Delimiter
PC
Frame 1
@ 0 0 W
Node Header
no. code
Frame 3
One word of data
Data from the same word is not divided.
FCS (Frame Check Sequence) When a frame is transmitted, an FCS is placed just before the delimiter or termi-
The largest block of data that can be transmitted as a single frame is 131 charac-
ters. A command or response of 132 characters or more must therefore be di-
vided into more than one frame before transmission. When a transmission is
split, the ends of the first and intermediate frames are marked by a delimiter
instead of a terminator.
As each frame is transmitted, the receiving node waits for the delimiter to be
transmitted. After the delimiter has been transmitted, the next frame will then be
sent. This procedure is repeated until the entire command or response has been
transmitted. The following diagram shows an example of host link communica-
tions addressed to a PC.
Frame2 (command)
Text
FCS
Delimiter
Delimiter
Precautions for Long Transmissions
When dividing commands such as WR, WL, WC, or WD that execute write op-
erations, be careful not to divide into separate frames data that is to be written
into a single word. As shown in the illustration below, be sure to divide frames so
that they coincide with the divisions between words.
D Data
Data
nator in order to check whether any data error has been generated. The FCS is
8-bit data converted into two ASCII characters. The 8-bit data is the result of an
EXCLUSIVE OR performed on the data from the beginning of the frame until the
end of the text in that frame (i.e., just before the FCS). Calculating the FCS each
Frame3 (command)
Text
FCS
Terminator
Delimiter
One word of data
Data from the same word is not divided.
: ↵
FCS Terminator
Section 11-2
Unit no.
Header code
End code
Text
FCS
Terminator
Frame (response)
↵
FCS Delimiter
405