Addressing - Siemens SINUMERIK 828D Function Manual

P4: PLC for SINUMERIK 828D
14.3 Programming
User data blocks are exclusively created by the user. If it is intended to indirectly access blocks of the same
structure, then these should be located one after the other regarding the numbering.
Special data blocks are permanently specified as far as their structure is concerned from the system and can be
found in the Programming Tool PLC828 in "Libraries". However, whether they are integrated in the user program,
assigned to a data class and loaded into the CPU is the responsibility of the user and his design philosophy (if
e.g. a maintenance planner is not used, then these do not have to be integrated as far as the DB is concerned).
14.3.2.3

Addressing

Direct addressing
For direct addressing, the
"Addressing range of the target system [Page 1100]").
The CPU memory (V, I, Q, M and SM) can be accessed bit by bit as well as in the byte, word and double-word
format. The direct address comprises the memory type and a valid address number.
To access a bit in a memory area, enter the byte address and the number of the bits. Separate the byte from the
bit using a decimal point.
Examples:
DB9900.DBX20.0
MB21,
QD16,
I1.7,
Indirect addressing
Indirect addressing can only be used for data blocks with the same structure (the same type). These are used so
that when accessing data blocks, the number of the data block can be variably addressed. The data block
number must be located in one of the accumulators AC0 ... AC3 (see "Data blocks [Page 1108]").
Absolute and symbolic addressing
You can specify the addresses in the operations in your program either absolutely or symbolically.
absolute address
An specifies the memory type and the address number.
symbolic address
A (briefly: symbol) specifies the address using a name (a combination of alphanumeric
characters).
Global symbols
are assigned in the symbol tables to their absolute address values and are valid throughout the
project (global). This assignment can be made at any time.
Local symbols
are assigned in the local variable table of the particular program and are only valid in this program
(local).
1102
memory type
as well as the
Bit 0 in byte 20 of DB9900
Flag byte 21
Output double word 16
Bit 7 in input byte 1
address number
must be specified (also refer to
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
Basic Functions