PDP-11/70 replica

It's been a while, lots have been happening at $dayjob, and time has been an issue lately (that, and funds for components)

I had ordered boards from PCBWay back in february, received them some time later, then time-crunch hit, and I had no time whatsoever to do anything on the project.

those boards are beautiful, look at them !

and here is the stencil...

Again, thank you very much to PCBWay for sponsoring this project with their PCBs

Now, I need to scrounge some money to give to DigiKey 🤣

Started designing an automated board tester.

I don't know what computer I should use, a Raspi Pico should be sufficient, but a full raspi could be better, dunno.

the video is here

There, I started to populate the DAP board, unfortunately, I am missing the 50-ish 16 legged sockets, so those will have to wait.

see the video here

Finally found some time (and money) to order the DAP boards from JLCPCB.

here they are in their purple glory (each part of the CPU will have a different color)

I started to assemble them but I messed up the reference of 2 resistor values in my digikey order, so I'll have to do another order for those...

Took some time today to install all the small components -- Resistors and Diodes -- on the chip tester pcb

will do the rest another day, i't getting too hot , have to turn off the light and soldering iron

In order to make sure everything works, I have ordered a Retro Chip Tester Pro from Stephan

https://8bit-museum.de/sonstiges/hardware-projekte/hardware-projekte-chip-tester-english/

which I just received.

Time to order the components to fill this very nice set of boards !

I made a new component for the board and gold fingers, and modified the first board to use it.

Also, I dumped it all into a new gitlab project.

enjoy !

I'll be ordering boards when some money shows up. will have more pictures then

There, took some time, but the first board (the DAP, DAta Paths) is fully routed

Turns out I was mistaken with the A=B situation.

The pins on the ALU are open collector, this does a wired AND, which is incredibly slow (as suspected).

So, what I had needs modified, and this appears to be more appropriate. The R11 / R12 value is debatable though, maybe the classic 1k value would be good enough ?

So, how do we go on doing this ?

Well, download the document here for the KB11-C processor boardand start page 1 😎

First board is the M8130 DAP (Data Paths) which contains the 16 bit integer ALU and related multiplexers.

Schematic capture is done.

There is one thing that looks wierd to me in the original schematic, namely, the ALU chips (74S181) A=B ouputs are tied together with a pair of resistors to pull the line up/down, sure looks like a wired or hack...

So I decided to add the possibility to replace this with proper or gates (a 74S02 would add 5.5ns, which I don't think is so much delay that it'd break things)

Same thing happens in the generation of "BUS A=B (15:08) H"

Of course, the board could be populated with more recent parts such as ACT for all functions that currently exist in this family.

I have now started routing the board. about 50% done right now.