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Build your own PDP 8I, Part 4..

Hi All;

Dave, Thank You for the information, I needed it..

"" Note that after the BIN loader has stopped - the accumulator should equal 0000 (otherwise an error has occurred).

The BIN loader contains a checksum - so it should know itself if the load has been successful or not... ""

That is good to know..

At present I have switched Computers, as the one I was using Might have been too slow to properly run Tera-term..
I think it may have had too much Background things running on it, as things were very slow and it has a fairly fast AMD processor in it and I am not going to mess with it at present..
I am Re-loading XP on this other machine, since it won't be on the network (www) I don't care that it is XP and I like XP anyway..

THANK YOU Marty
 
A slow PC is good!

The 'deadly sin' is sending character too fast to the -8 as it may miss them. Sending characters too slow is fine - there is no timeout on the received character within the RIM or BIN loaders.

Dave
 
Hi All;

Dave, Thanks for the warning..

What I was concerned about was a problem of running TeraTerm and sending of the Characters..
The PC seemed to get too bogged down..
Once I can safely send a file down to the -8 at 300 Baud and have the -8 process it and file it in Memory..
Then I would like to see IF I can get it to work at 600 or even 1200 Baud..
At present the -8 seems to run fine at 4800 Hz, and I think at 9600 Hz as well..
So, I am hoping that at 4800 that it gives it enough time to fully process it to Memory..
Who knows maybe I can crank it up to 19.2K HZ..
But, before that I want to add the second UART to the mix and have it working as well..

THANK YOU Marty
 
I suppose that's why we are building DEC PDP-8's - to get away from Windows (once again)...

I would advise getting your current -8 proven to be working before attempting something else. Just my humble opinion. Enjoy a bit of 'play time' with your creation - you deserve it...

Dave
 
Hi All;

Dave, Thanks for Your Humble opinion..

"" I would advise getting your current -8 proven to be working before attempting something else. Just my humble opinion. Enjoy a bit of 'play time' with your creation - you deserve it... ""

Yes, which is Why I am trying to get running the test programs that are provided..

I have Found a Mistake in my BIN Loader, and I am in the early part of the program..

Address '7633 should have '0274, but it has instead '0354..
I would say a bit slid..
I am still looking and copying it down into a notebook, and comparing it to the Listing..
At this point I don't know and can't say if it is faulty program originally or in the transferring of it to my PC, or the PDP 8i Memory itself..
Here are the Rest of the Mistakes..
Address '7672 should have '6016, but it has instead '6012..
Address '7673 should have '5265, but it has instead '6014..
Address '7674 should have '0300, but it has instead '5265..
Address '7703 should have '6214, but it has instead '6224..
Address '7754 should have '0000, but it has instead '0300..

So, if they are repeatable, I know where to fix the problem..

THANK YOU Marty
 
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Hi All;

M-Thompson, Thank You for the Reply..

"" Poly Basic will run on a 4k PDP-8/I. We use it with a 4k DECtape only PDP-8/I running DMS. ""

Where can I get Poly Basic and DMS for my enjoyment..
And can I just load these with either RIM or BIN ??

If I remember correctly the TI 990/10 I used to Run (At work) Had a DMS..
Don't know what it had, or what it did..

THANK YOU Marty
 
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POLY BASIC is DECUS 8-195. Documents available but can't find the software at the moment.

I think POLY BASIC requires some form of random access storage to run doesn't it (e.g. DF32/RF08/TU55)? I wonder if there are any other titles in the DECUS library - I will have a look.

Dave
 
Hi All;


Dave, Thank You for Your Answer..

I wonder If M-Thompson has anything or if what He has is Just an Image file..

"" I think POLY BASIC requires some form of random access storage to run doesn't it (e.g. DF32/RF08/TU55)? ""

Since I never heard of it before these postings, I have no idea.. But, You are most likely correct..

Dave, I have Sent You a Private Message..

THANK YOU Marty
 
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Hi All;

Thank You, M-Thompson, for the Information..

"" You do need a TC01/TC08 controller and DECtape to run the DMS operating system. It would be a bit of work to add the Posibus I/O bus to your system.

If you add 8k more memory and a second serial port you can boot OS/8 from a simulated RK05 disk drive.
See: https://github.com/drovak/os8diskserver ""

I do plan to add a Second Serial Port..
I just don't know How to add the additional Memory..

THANK YOU Marty
 
Marty said:
I just don't know How to add the additional Memory..
Click to expand...

You need to implement the MC8/I Extended Memory Controller. It is described in Volume II of the PDP-8/I Maintenance Manual. It adds three address lines so it supports up to 32k of memory.

There are IOT instructions that set the Data and Instruction fields. When a JMP or JMS instruction is executed the new Data and Instruction field value is used.

It is not very complicated, so it might not be difficult for you to implement.
 
Hi All;

M-Thompson, Thank You for the information..

I will need to look it up and see what it contains..

"" It is not very complicated, so it might not be difficult for you to implement. ""

I will take Your Word on that.. Thank You..

Where can I get a Schematic for this Board ??
I found this from BitSavers..
http://bitsavers.trailing-edge.com/pdf/dec/pdp8/pdp8i/DEC-8I-OptionsSchVol2_1970.pdf
Is this the right/correct one ??
Since the DEC-8I-HR1A-D doesn't show one, that I can see..
http://bitsavers.trailing-edge.com/pdf/dec/pdp8/pdp8i/DEC-8I-HR1A-D_8Imaint_Mar70.pdf
http://bitsavers.trailing-edge.com/pdf/dec/pdp8/pdp8i/DEC-8I-HR2A-D_8Imaint_May70.pdf
These are the links that I found, hopefully they are correct..

THANK YOU Marty
 
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Hello m_thompson,

can you tell us where Volume II of the maintenance manual can be found ? It does not seem to be present at bitsavers.
Thanks alot,

Gerhard Oed
 
Hi All;

I am putting the -8 away for awhile..

I am going to get out the PDP 11/45, and see what I can do for it..

And it's not that the PDP 8i clone hasn't been fun.. And alot of learning experience..
I will put the -8 away for awhile, but there is more for me to do on it..
I have notebooks to finish and update and a second TTY port to wire up..
And look into Memory Expansion, to it's max..
And this is the longest that I have worked on any one project, I think..

THANK YOU Marty
 
Marty,

I was tentatively looking at the second UART.

Here are my thoughts (references relative to the document "TTY Interface.pdf") before I implement them in LOGISIM.

A second serial port should be relatively easy (!). The first serial port is addressed as 03 (input) and 04 (output). The second serial port default is usually 40 (input) and 41 (output).

The logic on figure 2 (for TX) and figure 3 (for RX) can be duplicated for the second port with the exception of devices F14 and F15 decoding for the different IOT addresses.

The inverters for generating IOP1.H, IOP2.H and IOP4.H on figure 2 can be eliminated for the second port and wired directly to the output of the respective gates of E17.

You can also use the same baud rate generator device (assuming the same BAUD rate for both serial ports can be the same - not unreasonable).

You will have to make a slight 'tweak' to the logic on figure 1. G18 pin 8 and E12 pin 8 combines the SKIP and INTERRUPT signals from the transmit and receive half of the first serial port. As we are adding a second serial port - there will be 4 of these lines to accommodate. Either these gates will have to be modified to accommodate 4 separate inputs instead of 2 - or the new logic needs to be merged with the old.

There is also RDE.L and RDA.L sneaking back to the CPU logic. These will require gating with the second serial port so the CPU signal goes low when either of the corresponding signals from either serial port is activated.

There is an 'odd' signal lurking on figure 2 from pin 6 of E19 (DS.L). Not sure where that goes to yet.

Also found another gate on figure 3 that doesn't need duplicating - G17 pin 13. This output signal can be used directly by the second port.

I don't think (first pass) there are any other gotchas.

I have started to have a look at the memory management. I thought I would base my design on the PDP-8/e variant - but then realised that I am using the diagnostics for the PDP-8/I to test my LOGISIM implementation. There is a difference between the 8/I and 8/E implementation - so I might have to re-look at the 8/I implementation to be on the safe side. There is no point in me doing anything unless I can test to properly!

Dave
 
Hi All;

Dave, Thank You for Your Input, I am going to have to carefully look what You wrote in the above post and compare it to 'our' schematics..

And then get back to You, on this..

"" There is an 'odd' signal lurking on figure 2 from pin 6 of E19 (DS.L). Not sure where that goes to yet. ""
Pin 23 on the UART..

THANK YOU Marty
 
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Hello, guys. First post here :) I read this "Four Chapter Adventure" in non-stop mode. Looks like it was ended quite happily. But still few things not clear to me.
1) was 32K RAM implemented?
2) how about second TTY?
3) was is the total IC count for PDP8+I/O board?
4) what is the current drainage on +5V rail?
5) any attempts to overclock "CPU"?
6) what was uesd for last design registers 74175 or 74174?

I would like to jump on this train and "follow the way of jedi", but split whole circuit into a few functional units and m/b. I'm not orthodox, so would go with 74LSxxx IC's and 32K SRAM(no back-up battery). Any input/advice is appretiated.

Cheers
 
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