prefix_a16

prefix address 16 is an instruction prefix that causes all memory operations except instruction fetch to be performed on IO devices rather than on the main memory. Such memory accesses are called regular. prefix_a16 also causes every regular memory access to take two cycles instead of one.

It is guaranteed that no hardware interrupt occurs between prefix_a16 and the instruction after.

Instruction	Encoding	Semantics	Cycles
prefix_a16	10 000 000	enable $\mathit{addr}[16]$ for regular memory operations in the next instruction	1