Access Indirectly Addressed Registers: Using the Database

1. Use SI 40 Database Index to access a particular MI.
   For example, to access MI 2 you store the number 2 into SI 40.  

 

2. Use SI 41 Database Value to write a value into MI 2.
   For example, you can store a number value into SI 41.

 

When you use SI 41 Database Value in your program, the program actually reads the MI that is referenced by SI 40 Database Index.

Example 1: Write

In the net below, 0 is stored in SI 40 when the M90 OPLC is powered up. This means that integer 0 is now the current ‘database’ integer.

 

In the net below, the analog value contained in SI 20 is stored in SI 41 every second. According to the net above, the current ‘database’ integer is 0. The analog value is therefore stored in integer 0.  

 

In the next net, the value in SI 40 is incremented by 1every second, changing the current database integer. This means that the first analog value will be stored in integer 0, the second analog value in integer 1, and so on.

 

Example 2: Read

In the first part of the net below, 10 is stored into SI 40. Integer 10 is the ‘database’ integer.  In the second part of the net, the value in SI 41 is compared to the value in integer 4.  

The value in SI 41 is the value actually in integer 10—the current database integer.