!
53
Caution The node number assigned to a Host Link Unit on a Host Link System network is
called the “unit number” for the PC in the PC Setup and in the header portions of
command formats in the CV-series PC Operation Manual: Host Interface. When
coding commands for the Host Link Unit, be sure to use the node number and
not the unit number.
All commands and responses are transmitting in ASCII. Be sure that the data is
in the correct form (BCD or hexadecimal) before converting it to ASCII for trans-
mission. Data is handled in hexadecimal unless otherwise specified.
4-3-1 Communications Protocol
The host computer has the initial right to send. Data transfer between the host
computer and the Host Link System is therefore initiated when the computer
sends a command to a PC in the Host Link System. The arrows in the following
diagram illustrate transfer of the right to send. Each command and each re-
sponse is sent as a block, with longer block divided into two or more frames, as
described in more detail later. Responses cannot be split into multiple frames.
FCS
FCS
FCS
FCS
Node No.
Command block
Header
Text
Terminator
Node No.
Header
Text
Terminator
PC
Node No.
Header
Text
Delimiter
First frame
Delimiter
Next frame transmission
enabled
Text
Terminator
End frame
Node No.
Response block
Header
Text
Terminator
Host computer
Response block
Command block
FCS
4-3-2 Blocks
Data is sent in a Unit called a block. The data block sent from the host computer
to the Host Link System is called a command block. The block returned from the
PC to the computer is called a response block. The terminator in the command
block enables the PC to send a response. The terminator in the response block
enables the host computer to send another command.
Block Format
@
xx
xx xx
Node
No.
Header Text FCS Terminator
s
x 10
0
x 10
1
FCS calculation range (refer to page 56)
*
C-mode Commands Section 4-3
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