Base register instructions

The USING and DROP assembler instructions enable you to use expressions representing implicit addresses as operands of machine instruction statements, leaving the assignment of base registers and the calculation of displacements to the assembler.

In order to use symbols in implicit addresses in the operand field of machine instruction statements, you must:

Code a USING instruction to assign one or more base registers to a base address or sequence of base addresses
Code machine instructions to load each base register with the base address

Having the assembler determine base registers and displacements relieves you of the need to separate each address into an explicit displacement value and an explicit base register value. This feature of the assembler eliminates a likely source of programming errors, thus reducing the time required to write and test programs. You use the USING and DROP instructions to take advantage of this feature. For information about how to use these instructions, see USING instruction and DROP instruction.