HLASM: V1R6 Language Ref

DROP instructionLabeledDependentIf neither base_register nor label is specified in the operand of a DROP instruction,all active base registers assigned by ordinary, labeled, and labeled dependentUSING instructions are dropped.After a DROP instruction:v The assembler does not use the register or registers specified in the DROPinstruction as base registers. A register made unavailable as a base register by aDROP instruction can be reassigned as a base register by a subsequent USINGinstruction.v The label or labels specified in the DROP instruction are no longer available assymbol qualifiers. A label made unavailable as a symbol qualifier by a DROPinstruction can be reassigned as a symbol qualifier by a subsequent labeledUSING instruction.The following statements, for example, stop the assembler using registers 7 and 11as base registers, and the label FIRST as a symbol qualifier:DROP 7,11DROPFIRSTUSINGYou cannot end the domain of a labeled USING instruction by coding a DROPinstruction that specifies the same registers as were specified in the labeled USINGinstruction. If you want to end the domain of a labeled USING instruction, youmust code a DROP instruction with an operand that specifies the label of thelabeled USING instruction.USINGTo end the domain of a dependent USING instruction, you must end the domainof the corresponding ordinary USING instruction. In the following example, theDROP instruction prevents the assembler from using register 12 as a base register.The DROP instruction causes the assembler to end the domain of the ordinaryUSING instruction and the domains of the two dependent USING instructions. Thestorage areas represented by INREC and OUTREC are both within the range of theordinary USING instruction (register 12).USING *,12USINGRECMAP,INRECUSINGRECMAP,OUTREC..DROP 12..INREC DS CL156OUTREC DS CL156To end the domain of a labeled dependent USING instruction, you can code aDROP instruction with the USING label in the operand. The following exampleshows this:USING *,12PRIOR USING RECMAP,INRECPOST USING RECMAP,OUTREC..DROPPRIOR,POST172 HLASM: V1R6 Language Ref