间接寻址与地址寄存器.ppt

Indirect Addressing and Address Register Instructions Addressing Possibilities with STEP 7 Direct Addressing of Variables Direct Addressing of Address Identifiers in DBs Evaluating DB Information in the Program Instructions with DB Registers: CDB: Exchange DB Registers Load DB Register in ACCU1 L DBNO (load opened DB number in ACCU1) L DINO (load opened DI number in ACCU1) Load length of data blocks L DBLG (load the length/bytes of the opened DB in ACCU1) L DILG (load the length/bytes of the opened DI in ACCU1) Memory Indirect Addressing Structure of Pointers with Memory Indirect Addressing Special Features of Memory Indirect Addressing Address Areas for Storing 16-bit and 32-bit Pointers: Bit Memories (addressed absolute or symbolic, e.g.: OPN DB[MW30], OPN DI[Motor_1], etc. A I[MD30], T QD[Speed_1], etc.) Local Data Stack (addressed absolute or symbolic,e.g.: OPN DB[LW10], OPN DI[#DB_NO], etc. A I[LD10], T QD[#Par_Pointer], etc.) Global (Shared) Data Block (can only be addressed absolute, DB must be opened beforehand,e.g.: OPN DB[DBW0] (overwrites DB register !!!), OPN DI[DBW22], etc. A I[DBD10], T QD[DBD22], etc.) Instance Data Block (can only be addressed absolute, DI must be opened beforehand,e.g.: OPN DB[DIW20], OPN DI[DIW0] (overwrites DI register !!!), etc. A I[DID10], T QD[DID22], etc.) Characteristics in the Passing of Pointers to FBs and FCs Pointers passed in parameters cannot be used directly for memory indirectaddressing. Pointers passed for memory indirect addressing must be copied into temporary variables before accessing. Example of Indirect Addressing Exercise 4.1: Loop Programming with Indirect Addressing Area-Internal, Register Indirect Addressing Area-Crossing, Register Indirect Addressing Instructions for Loading Address Registers Loading the Address Register LARn (n =1 or 2): Load contents of ACCU1 in ARn LARn Address Load contents of Address in ARn LARn P#Address Load address of Address in ARn Address: Processor re