S7-200 addressing method in PLC programming

       In the S7-200 series, addressing modes are divided into two kinds: direct addressing, and indirection. Direct addressing mode is used directly in the instruction memory or registers the component name and address number, direct to find the data. Indirect addressing is the address pointer is used to access data in the memory, before use, first memory address into the address of the unit where the data pointer register, then, according to this address to access the data. This book only direct addressing.
When addressed directly, the address of the operand shall be in the specified format. Data type should match the consistent instruction in the instruction.
In the S7-200 series, can be bit, byte, Word and double word address of the storage unit. When addressing, data address begins with a letter representing the storage type, followed by a tag that represents the data length, then the memory cell number; for-bit addressing, you also need to refer to position number after the separator.
Represents the data length, respectively with the letters b, w and d as byte, Word and double word identifier.