Siemens SINUMERIK 828D Function Manual page 891

Figure 13-15 DB 20
Note
If the number of PLC machine data used is increased later, then DB20 must be deleted
beforehand. To prevent such extensions in use having any effect on the existing user
program, the data in DB20 should be accessed in symbolic form wherever possible, e.g. by
means of a structure definition in the UDT.
Interrupts
400120 Delete DB 20 in PLC and restart
Explanation DB length is not the same as the required DB length
Response Interrupt display and PLC Stop
To correct or Delete DB 20 followed by RESET
avoid errors
Continuation After cold restart
Example
The project in the example requires 4 integer values, 2 hexadecimal fields with bit information and 1 real value.
Machine data:
MD14510 $MN_USER_DATA_INT[0]
MD14510 $MN_USER_DATA_INT[1]
MD14510 $MN_USER_DATA_INT[2]
MD14510 $MN_USER_DATA_INT[3]
...
MD14512 $MN_USER_DATA_HEX[0]
MD14512 $MN_USER_DATA_HEX[1]
...
Basic Functions
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
P3: Basic PLC Program for SINUMERIK 840D sl
13.8 Structure and functions of the basic program
123
456
789
1011
12
AC
891