4. FUNCTIONS
MELSEC-A
4-1
4. FUNCTIONS
4.1
Functions for Exchanging with Slaves
The main function in the AJ71PB92D/A1SJ71BP92D is for exchanging I/O data with slave stations
connected to the PROFIBUS-DP network. The method used for this exchange is to read/write the I/O
image in the buffer memory using FROM/TO instructions.
A schematic drawing of this exchange function is as follows.
CPU module
AJ71PB92D/
A1SJ71PB92D (Class 1 master)
FROM
TO
Buffer memory
Input
image
Output
image
Input
image
Output
image
Input image
Input image
Output image
Output image
PROFIBUS-DP network
Slave station
4.1.1
Exchange flow
The I/O data exchange flow with slave station is shown below.
* The buffer memory refresh with the FROM/TO instructions is conducted asynchronously.
Set the slave trouble information cancel area.
(Setting is unnecessary if the default value can be left
unchanged.)
Communication trouble area type selection
(This setting is unnecessary if the default value can
be left unchanged.)
Write the initial OUTPUT data value in
the output area.
Turn ON the exchange start request signal (Y00).
Check that the exchange start/end
signal (X00) is ON.
Read the input data from the input area
using the FROM instruction.
Write the OUTPUT data in the output area in the
buffer memory using the TO instruction.