High Level Assembler - Opcodes overview, Millicode Extension set A3

The table below lists all documented opcodes in extension set A3 for IBM mainframe processors. Each opcode links to a text section with some additional info on the pertinent opcode.

Opcode Assignments.

Please note that the creation of descriptions for all individual instructions is an ongoing process. As yet no such descriptions have been created for the opcodes on this page.

Extension Set A3 - Millicode Instructions

All instructions in this table are four bytes in length. The first byte always has a value of X'A3', the second half of the second byte designates the exact instruction.
Information on millicode-only instructions is very limited. What you find here has been gleaned from various IBM patents. Some of these patents appear to contain some errors, or maybe even intentional obfuscation. For example, the instruction LTA is said to have opcode X'A25' but it is the only known instruction in the range X'A20' through X'A2F'. In the range X'A30' through X'A3F' however, many millicode-only instructions can be found. The fact that opcode X'A35' seems to be unassigned suggests that X'A25' for LTA may well have been a typo, and maybe should have been X'A35'.

A3 0 1 2 3 4 5 6 7 8 9 A B C D E F
      WSRS         TPSW    


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