On Mon, 22 Apr 2024 at 09:50, Seymour J Metz <[email protected]> wrote: > IBM promised to never use opcode 00, and that's what I use when I want > (E)SPIE in the skie. >
But way back when (around the last S/370 PofO they said "The operation code 00, with a two-byte instruction format, and the set of sixteen 16-bit operation codes B2E0 to B2EF, with a four-byte instruction format, are allocated for software uses where indication of invalid operation is required. It is improbable that these operation codes will ever be assigned to an instruction implemented in the CPU." Then at some point (z10 era?), they defied improbability and used some of the B2Ex opcodes. You'd think it wouldn't have killed them to keep a range of just 16 two-byte opcodes available for customers. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
