Non-modal instructions

An instruction that behaves the same, regardless of the AMODE of the program, is called a non-modal instruction. The only influence AMODE exerts on how a non-modal instruction performs is where the storage operand is located. Two excellent examples of non-modal instructions have already been described: the Load and the Add instructions. Non-modal z/Architecture® instructions already described also include the LG instruction and the AGF instruction. For example, programs of any AMODE can issue AG R3,NUM64, described earlier, which adds the value of a doubleword binary integer at location NUM64 to the contents of GPR3, placing the sum in GPR3.

The LGF instruction is another example of a non-modal instruction. In LGF R3,MYDATA, assume MYDATA is a signed negative binary integer. This instruction places MYDATA into the low-order half of GPR3 and propagates the sign (1s) to the high-order half, as follows:

If the current AMODE is 64, MYDATA can reside anywhere in the address space; if the AMODE is 31, MYDATA must reside below 2 gigabytes; if the AMODE is 24, MYDATA must reside below 16 megabytes.

Other 64-bit instructions that are non-modal are the register form of AGF, which is AGFR, and the register form of LGF, which is LGFR. Others are LGR, AGR, ALGR, and ALG.