Host Link Communications; Protocol - Omron CQM1H-SCB41 Operation Manual

Host Link Communications

4-4

Host Link Communications

4-4-1

Protocol

Command Frame Format
@ x 10 1
Node No.
Normal Response Frame
Format
1 0
x 10 x 10
@
Node No.
Host Link communications are executed by means of an exchange of com-
mands and responses between the host computer and the PC. The command
or response data that is transferred in one exchange is known as a frame and
one frame can contain up to 131 characters of data.
The frame formats for Host Link commands transmitted from the host com-
puter and responses returned from the PC are described below. The PC auto-
matically returns an ASCII-code response when it receives an ASCII-code
command from the host computer. The host computer must have a program
that controls the transmission and reception of the commands and responses.
When transmitting a command from the host computer, prepare the command
data in the format shown below.
x 10 0
Header
code
The header code and text depend on the Host Link command being transmit-
ted. When a compound command is transmitted, there will be a second sub-
header code.
The FCS (Frame Check Sequence) code is calculated at the host computer
and set in the command frame. The FCS calculation is described later in this
section.
The command frame may be up to 131 characters long. A command of 132
characters or more must be divided into more than one frame. To split the
command, use a carriage return delimiter ( , CHR$(13)) instead of a termina-
tor. A terminator must be used at the end of the last frame.
When dividing commands such as WR, WL, WC, or WD that execute write
operations, be careful not to divide into separate frames data that is to be writ-
ten into a single word. You must divide frames so that they coincide with the
divisions between words.
Item
@ An "@" symbol must be placed at the beginning of every command.
Destination Identify the PCs by the Host Link node numbers (0 to 31) set in DM
Node No. 6558 and DM 6553 of the PC Setup.
Header code Set the 2-character command code.
Text Set the command parameters.
FCS Set a 2-character Frame Check Sequence code.
Terminator Set two characters, "*" and the carriage return (CHR$(13)) to indicate
the end of the command.
A normal response from the PC is returned in the format shown below. Pre-
pare a program at the host so that the response data can be interpreted and
processed.
1 0
x 16 x 16
Header End code
code
The header code and text depend on the Host Link command that was
received. The end code indicates the completion status of the command (e.g.,
whether or not an error has occurred).
Text FCS
Function
Text
Section 4-4
Terminator
FCS Terminator
45