## ALP Programming Guide and Reference

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### ALP3506: Register combination invalid with -bit expression

For 80386 processors or greater, both 16-bit and 32-bit effective addresses are supported, but the two modes differ in the register combinations that are allowed for indirect addressing. The expression used a combination that was invalid for the referenced address size.

For expressions that refer to 16-bit (USE16) memory locations, only a single base register (BX or BP) and/or a single index register (DI or SI) may be used.

For expressions that refer to 32-bit (USE32) memory locations, only a single base register (EAX, EBX, ECX, EDX, ESP, EBP, EDI, ESI) and/or a single index register (EAX, EBX, ECX, EDX, EBP, EDI, ESI) may be used; no single register may appear more than once in a given expression.