Yokogawa JUXTA M Series Digital Limit Alarms MVTK - Manual (Page 48)

5-2
<Toc> <Ind> <5. MODBUS Communication >
IM 77J04J11-01E 1st Edition : 2006.08.25-00
5.1.1 Configuration of Message
Messages sent from a higher-level device to the M Series consist of the following elements.
Number of bytes in RTU mode None
Number of bytes in ASCII mode 2 2
(1) (3) (4) (5) (2) (6)
Element Address
Number
(ADR)
Function Code Start of
Message Mark
Data Error Check End of
Message Mark
None
1 2 2 4n
1 1 2n 2
(1) Start of Message Mark
This mark indicates the start of a message. Note that only ASCII mode requires a
colon (:).
(2) Address Number (01 to 99)
Address numbers are used by a higher-level device to identify the M Series at the
communication destination. (Identification numbers specific to individual M Series,
which is expressed in hexadecimal in the message.)
(3) Function Code (See subsection 5.2.1, "List of Function Codes.")
This specifies a command (function code) from the higher-level device.
(4) Data
This specifies D register numbers, the number of D registers, parameter values, or
others in accordance with the function code. (It is expressed in hexadecimal in the
message.)
(5) Error Check
In RTU mode : Carried out by the cyclic redundancy check (CRC-16) system.
In ASCII mode : Carried out by the longitudinal redundancy check (LRC) system.
(6) End of Message Mark
This mark indicates the end of a message. Note that only ASCII mode requires CR +
LF.