Touché.

Charles

-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf 
Of Tom Marchant
Sent: Wednesday, July 13, 2016 5:50 AM
To: [email protected]
Subject: Re: Error in a simple COBOL program

On Tue, 12 Jul 2016 14:19:26 -0700, Charles Mills wrote:

><pedantry>
>
>The op code is ... just a binary byte in any event, not hex.

In some cases there are more bits than the first byte of an instruction that 
are part of the opcode. Opcodes can be 8, 12, or 16 bits, depending on the 
instruction. The first 8 bits of the opcode are always in bits 0-7 of the 
instruction. Bits 8-11 of a 12-bit opcode are always in bits 12-15, and bits 
8-15 of a 16-bit opcode are either in bits 8-15 or bits 40-47, depending on the 
value in the first 8 bits. For example, if the byte in bits 0-7 contains X'E3', 
the remaining bits of the opcode are in bits 40-47.

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