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Changing a plain PDP-11/23 into a PDP-11/23+

Let me know if you can get the FPU to do something, I never have had anything different happen with or without it. Something like back in the old days when you had a 286 and went out and bought the math co- processor, you would plug the chip in and turn the system on expecting something to happen or be different but then after going thru all the stuff with doing it someone always comes up and then tells you “Kid, you need software written to use that chip first” But it does look good to see all the sockets full on the board.
Too bad the other card went for so much, imagine it would have been a good deal if it had the serial cables or if it was guaranteed or something. Wonder if anyone here bought it?
 
Qbus said:
Let me know if you can get the FPU to do something, I never have had anything different happen with or without it.
Click to expand...

I received my FPU yesterday and had the chance to install it onto my M8186 processor board today. It was not perfectly obvious to me where pin 1 was, so I Googled for some images of M8186 boards with the FPU installed. Was I surprised to get images with the chips plugged into the board in both directions! I finally settled on a couple of pictures that showed the CPU plugged in the same way as mine is, and the FPU "matching" that orientation. I took a deep breath and fired up my system, and I was greeted with the normal START? message. Whew! At least I have not blown everything up.

I took a record of the SHOW ALL command before and after the installation:

PDP-11/23 before FPU installation:

Code: 
RT-11SJ  V05.03  

.SHOW ALL

RT-11SJ  V05.03  
Booted from DU0:RT11SJ

USR   is set SWAP
EXIT  is set SWAP
KMON  is set NOIND
TT    is set NOQUIET
ERROR is set ERROR
SL    is set OFF
EDIT  is set KED
KMON nesting depth is 3

PDP 11/23 Processor
128KB of memory
Extended Instruction Set (EIS)
Memory Management Unit
60 Cycle System Clock                  

FPU support

Device    Status          CSR     Vector(s)
------    ------          ---     ---------
  CR      Not installed  177160   230
  CT      Installed      000000   260
  DD      Installed      176500   300 304
  DL      Not installed  174400   160
  DM      Not installed  177440   210
  DP      Not installed  176710   254
  DS      Not installed  172040   204
  DT      Not installed  177340   214
  DU      Resident       172150   154

<...snip...>

PDP-11/23 after FPU installation:

Code: 
RT-11SJ  V05.03  

.SHOW ALL

RT-11SJ  V05.03  
Booted from DU0:RT11SJ

USR   is set SWAP
EXIT  is set SWAP
KMON  is set NOIND
TT    is set NOQUIET
ERROR is set ERROR
SL    is set OFF
EDIT  is set KED
KMON nesting depth is 3

PDP 11/23 Processor
128KB of memory
FP11 Hardware Floating Point Unit              <---  WHOO HOO !!!
Extended Instruction Set (EIS)
Memory Management Unit
60 Cycle System Clock                  

FPU support

Device    Status          CSR     Vector(s)
------    ------          ---     ---------
  CR      Not installed  177160   230
  CT      Installed      000000   260
  DD      Installed      176500   300 304
  DL      Not installed  174400   160
  DM      Not installed  177440   210
  DP      Not installed  176710   254
  DS      Not installed  172040   204
  DT      Not installed  177340   214
  DU      Resident       172150   154

<...snip...>

Ahem... The "WHOO HOO" part was added by me. 8-)

I am assuming this means that the query to the FPU during the boot process was answered properly, indicating at least the chip is properly installed and will attempt to run when called upon.

I tried a few things, but there is no difference, as I expected. I surmise that unless I actually have some code that contains the specific instructions that request assistance from the FPU, nothing will be obvious, except perhaps a bit more power consumption.

Apart from the "coolness factor," there's nothing much to see here. I now have three of the four possible 40 pin slots filled on my M8186 processor.

smp
 
Last edited:
The big thing the 11/23+ has over the 11/23 is that you can put a CIS chip and a KEF11 (or FPF11) in at the same time. I have two 11/23+'s with CIS, it was cool for Cobol/Dibol but that's about it.

The first run of 11/23 CPUs could only do 18 bits, but all the C rev or later ones (every board I have seen) can handle 22.
 
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