PDP-11 Integer Divide Instruction "Div", To: General Discussion: On-Topic and Off-Topic Post

Jerome H. Fine jhfinedp3k at compsys.to
Sat Feb 25 22:01:16 CST 2006

 >Don North wrote:

> [Snip]
> In most cases however it appears that if DIV overflows the quo and rem 
> registers are unaltered and the Vbit is set.
> SIMH and a real 11/44 (mostly) behave this way. The behavior below 
> found by Jerome may be an anomaly seen in E11.

Jerome Fine replies:

I responded to the first portion of this post about a week ago.
Shortly after that, John Wilson became directly involved and
clarified that E11 performs the calculations and "changes" the
registers even if the overflow "v" bit is set = 1.

If anyone is interested, John Wilson has posted a sample "plugin"
for E11 at:
in the files: inst.*

Since I am not a PC capable person, I don't have the software tools
to even assemble and link the plugin to produce a DLL file, let along
check out the plugin code.

However, I wrote some additional code for other UMul instructions
along with some UDiv instructions.  If anyone is capable on 386
assembly language instructions, I would be VERY grateful if a quick
look at my code seems reasonable.

John Wilson has suggested using http://www.openwatcom.org/ to
provide a WASM and WLINK to produce a DLL.  Is anyone
interested in helping me assemble and link the INST.ASM file?

I did not include my additions to the INST.ASM file, but I can
certainly post them to cctalk if there is any interest.

Sincerely yours,

Jerome Fine
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