User Manual

3.5 I/O Expansion of PLC applications
COM2:RS-485
7521 series
PLC
COM1:RS-232
7000 series
There is a Man Machine Interface in most PLCs. This interface is
originally designed for MMI applications. The 7521 series can use this
interface to build a bridge between PLC & 7000 modules.
The 7521 series can directly read/write the internal memory of the PLC.
Therefore the PLC can access the 7000 input modules as follows:
1. The 7521 series sends commands to the 7000 input modules
2. The 7521 series writes this data to the PLC’s internal memory
3. The PLC accesses this data from the internal memory
The PLC can control the 7000 output modules as follows:
1. The PLC writes data to its internal memory
2. The 7521 series reads this output data from the PLC’s memory
3. The 7521 series sends commands to the 7000 output modules
In this way, the input data of the 7000 modules can be shown on the touch
screen. Also, the user can control the output of the 7000 modules from the
touch screen.
7521/2/2A/3/4/7 Series Hardware User’s Manual, Ver. 1.5 Sep/2002, 7Mh-001-15 -----69