Yokogawa JUXTA M Series Digital Limit Alarms MVTK - Manual (Page 16)

3-2
<Toc> <Ind> <3. PC Link Communication >
IM 77J04J11-01E 1st Edition : 2006.08.25-00
3.1.1 Configuration of Command
Commands sent from a higher-level device to the M Series consist of the following ele-
ments.
Number of Bytes 1 2 2 1 3 2 1 1 Variable length
(1) (2) (3) (4) (5) (7) (8) (9) (6)
Element STX Address
number
(ADR)
CPU
number
01
Time to wait
for response
0
Command Data
corresponding
to command
Checksum ETX CR
(1) STX (Start of Text)
This control code indicates the start of a command. The ASCII code is 02 in hexadeci-
mal.
(2) Address Number (01 to 99)
Adress numbers are used by a higher-level device to identify the M Series at the
communication destination. (Identification numbers specific to individual M Series.)
(3) CPU Number
This is fixed to 01.
(4) Time to Wait for Response
This is fixed to 0.
(5) Command (See subsection 3.2.)
This specifies a command to be issued from the higher-level device.
(6) Data Corresponding to Command
This specifies an internal register (D register or I relay), number of data pieces and
others.
(7) Checksum
This converts the ASCII codes of texts between the character next to STX and the
character immediately before the checksum into hexadecimal values and adds them
byte by byte. It then fetches the single lowermost byte of the added results as the
checksum.
This column is only required for PC link communication with checksum. PC link
communication without checksum does not require this 2-byte space of ASCII code.
(8) ETX (End of Text)
This control code indicates the end of a command string. The ASCII code is 03 in
hexadecimal.
(9) CR (Carriage Return)
This control code indicates the end of a command. The ASCII code is 0D in hexadeci-
mal.
CAUTION
The control codes STX, ETX and CR are essential for commands when you create a
communication program for PC link communication. Omission of any of them or incorrect
order of them results in communication failure.