Melsec-A Protocol - YASKAWA MP920 User Manual

MEMOBUS Protocol Functions
Function
Code
01H
02H
03H
04H
05H
06H
08H
0FH
10H
3.2.3

MELSEC-A Protocol

The MELSEC-A protocol is used for communications between MELSEC-A Series general-
purpose sequencers manufactured by Mitsubishi Electric Corporation. There is no need to be
aware of the communications protocol. In this case, a special-purpose Ethernet Module
(AJ71E71) and a Computer Link Unit (AJ71UC24) are required for the Mitsubishi
MELSEC-A Sequencers.
Communications Using the MELSEC Protocol
The MELSEC protocol is used for communications between a Controller and a MELSEC-A
sequencer.
That is to say, the Master (Controller) transmits the MELSEC format instructions to the Slave
(MELSEC), and receives a response message from the Slave.
When communicating with a MELSEC-A computer, the protocol is automatically converted
inside the 217IF and the 218IF Modules. Therefore, the MSG-SND and MSG-RCV system
functions can be used in the same way as when the Extended MEMOBUS protocol is used by
a user program.
The following three MELSEC functions are supported by Ethernet communications using the
218IF and the AJ71E71:
• Communications between CPUs
• Fixed buffer communications
• Random access buffer communications
With fixed buffer communications, the Controller can be either a Master or a Slave. With
communications between CPUs and random access buffer communications, however, the
Controller will be a Master due to the MELSEC specifications.
With serial communications using the 217IF and the AJ71UC24, the special protocol type 1
is supported. With serial communications, the Controller will be the Master.
Function
Coil status read
Input relay status read
Holding register write
Input register read
Single coil status change
Single holding register write
Loopback
Multiple coil status change
Variable register write
3-7
3.2 Protocol Functions
No. of Points Remarks
−
2,000 points
−
2,000 points
−
125 words
−
125 words
−
1 point
−
1 word
− −
−
800 points
−
100 word
3