mitsubishi - Al Kossow's Bitsavers

MITSUBISHI MICROCOMPUTERSM50740~XXXSPSINGLE·CHIP I·BIT CMOS MICROCOMPUTERAddressing ModesThe M50740-XXXSP has 17 addressing modes and an extremelypowerful memory access capability.When extracting data required for arithmetic and logic operationsfrom the memory or when storing the results ofsuch operations in a memory using the appropriate instructionsfor this purpose, the memory address must be specified.Even when jumping to an address during a program,that particular address must be specified. The specificationof the memory address is called addressing., The data requiredfor addressing and the registers involved are nowdescribed. The M50740-XXXSP's instructions can be classifiedinto three kinds, as shown in Fig. 15, by the byte numberin the program memory required for configuring the instruction:1-byte, 2-byte and 3-byte instructions. In eachcase, the first byte is known as the "operation code" whichforms the basis of the instruction. The second or third byteis called the "operand" which affects the addressing. Thecontents of index registers X and Y also effect the addressing.However many the addressing modes, there is no differencein the sense that a particular memory is specified.What differs is whether the operand or the index registercontents or a combination of both should be used to specifythe memory or jump destination. Based on these 3 methods,the range of variation is increased and the M50740-XXXSP'soperation is enhanced by combinations of the bit operationinstructions, jump instruction and arithmetic instructions.The accumulator or register is specified with a 1-byte instructionand so there is no operand byte, which is the partspecifying the memory.Actual addressing modes are now described by type.IIl-byte instruction 2-byte instruction 3-byte instruction-.----.... -......---....OpcodeI Operand I IOpcodeI Operand I I... I Operand II IIIIIIndex registerxy"""-1,...00Fig.15Instruction byte configuration• MITSUBISHI.... ELECTRIC3-15