3.2 Protocol Functions
3-7
3
MEMOBUS Protocol Functions
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
Code
Function No. of Points Remarks
01H Coil status read 2,000 points
−
02H Input relay status read 2,000 points
−
03H Holding register write 125 words
−
04H Input register read 125 words
−
05H Single coil status change 1 point
−
06H Single holding register write 1 word
−
08H Loopback
−−
0FH Multiple coil status change 800 points
−
10H Variable register write 100 word
−
To Next Page
Loading...
