PDP-8 diagnostic tests

[Don North]

On 8/23/2016 12:31 PM, Scott Baker wrote:
> Hi,
>
> I have written a PDP-8 VHDL model and I have it running in an FPGA
> https://github.com/scottlbaker/PDP8-SOC
>
> At this time it has passed a basic DEC diagnostic instruction test but
> I found some interesting things when getting that instruction test to pass.
> For example:
>
> The following segment of code implies that IAC instruction affects the Link
> bit
>
>   1797             /GROUP 1 OPERATE TEST 33
>   1798 02626 7300          CLA CLL         /AC=0000 LINK=0
>   1799 02627 1053          TAD K2525               /AC=2525
>   1800 02630 7261          CLA CMA CML IAC /TEST COMBINATION
>   1801 02631 7420          SNL
>   1802 02632 7430          SZL
>   1803 02633 7402          HLT             /CLA CMA CML IAC FAILED, AC SHOULD
>   1804                                     /BE 0000, LINK SHOULD BE ZERO
>
> but the PDP-8 Handbook  ; DEC copyright 1966; page 14
> says nothing about the Link bit being affected by the IAC instruction.
>
> The simh PDP-8 simulator also shows that L is affected by IAC.
>
> If I change this test line from
>
>   1800 02630 7261          CLA CMA CML IAC /TEST COMBINATION  << link=0
>
> to:
>
>   1800 02630 7261          CLA CMA CML  /TEST COMBINATION  << link=1
>
> Can anyone point me to:
>
> 1) DEC documentation which more fully describes all the instruction set (in
> more detail  than the PDP-8 handbook)
>
> 2) Some more instruction tests in assembler source code format. I have
> found lots of binary files but I would prefer assembler source code format.
> I am using a pal compatible cross assembler.
>
> Thanks and Regards,
> Scott
>
Both TAD and IAC effectively perform 13 bit additions on {L,AC}.

The PDP-8a Handbook 
http://bitsavers.trailing-edge.com/pdf/dec/pdp8/handbooks/MinicomputerHandbook_1976.pdf
describes TAD operation on p5-3, and IAC operation on p5-6.

The PDP-8 handbooks are probably the best / only definitive architectural 
specification.

The PDP-8e processor maintenance manual:

http://bitsavers.trailing-edge.com/pdf/dec/pdp8/pdp8e/DEC-8E-HMM1A-D-D_PDP-8e_Maintenance_Manual_Volume_1_Processor_Sep73.pdf

is a pretty detailed implementation reference. Chapter 3 section 2 is a very 
detailed reference on the instruction fetch/decode/execute flow.

Don