Category Archives: Blog posts

Retrochallenge 2016/2 – Interak keyboard

So RC is upon us and I have decided to replace the failed keyboard on my newly acquired Interak-1 with a modern USB item.

The Interak keyboard uses a 7 bit parallel interface to present an ASCII character to machine itself with a strobe line to say that the data is ready. It’s a bit much to ask the Interak to cope with USB directly and it’s a bit much for me to learn enough about USB to be able to program a Z80 to cope in the time allowed and I don’t want to.

161001-img_20161001_181323Enter HobbyTronics who produce a small USB host board that just needs 5v and a USB keyboard and will produce a serial output.

The serial output can’t go straight in to the Interak either but serial to parallel isn’t too bad.

Enter Arduino.

161001-img_20161001_205049So, here we have an Arduino UNO with a prototype shield and a tiny USB keyboard. At the moment it’s just reading the serial input from the keyboard adapter and squirting it down the serial port to the PC but it’s a start.161001-img_20161001_205115 Next is to set up some pins for the parallel interface.

Keep watching (if you want).

Retrochallenge 2016/2 – Throwing my hat into the ring.

It’s Retrochallenge time again and how quickly it comes around and how ill-prepared I am.

Recent competitions have seen great entries by talented retro-folks the world over whereas my contributions have been less glorious but filled with enthusiastic zeal.

This time around will be no different πŸ™‚

I’m not sure what I will do to be honest. I may take a broken retro system down from the “shelf of good intentions” and try to fix it. I may try and interface a ZX printer to something non-Sinclair or perhaps get the Tandy 4 colo(u)r plotter talking to my PDP-11. Who can say?

Whatever happens there will be joy and frustration but mostly joy.

In the words of poppy-funster “Jem”

It’s just a ride, it’s just a ride
No need to run, no need to hide

Though there may be a need to solder…

See you on the other side.

 

Retrochallenge 2016 – End of the line. All change.

Well, another RC comes to an end an if there’s any truth in the saying “It’s not the winning, it’s the taking apart” then all is well. If, however, it is the winning then we have another “success deficit” on our hands.

So far I have the VT-180 in pieces. I looked at a few signals on the video board and compared them to those marked on the schematic but they all looked fine (see the photos).

160116-IMG_20160116_181840 160116-IMG_20160116_181754 160116-IMG_20160116_181725So next up I wondered if the 2114 static RAM chips have failed. I’ve seen them go on my DEC Rainbow and also on a Commodore PET a friend of mine has, so it’s quite common really. It would explain the garbled output.

One thing I like about DEC kit is it’s well made. The downside is that they used a lot of solder and getting chips out of any DEC board I’ve ever worked on is very difficult. So, as the last few hours of RC2016-1 tick away I have3 chips out, new ones on order and crud to clean out of the holes in order to add sockets.

The nice thing about Retrochallenge is there’ll be another one passing by any minute now.

Retrochallenge 2016 – Week 1 done. Some progress.

So here we are, one week in to RC2016-01 and what do we have to show for it?

As you saw in my previous post, I have taken the lid off the VT180 and it sits as a bare metal cage while I try to figure out what’s wrong.

151231-IMG_20151231_174248The initial display (shown on the left) has changed and is less verbose.Β 160106-IMG_20160106_194827 I’m not sure what happened to trigger the change.

The screen display is no longer in sync and rolls very quickly.

In order to help with the repair I have taken the VT100 board out of the card cage and I have it plugged in to the cable that was powering the card edge connector on the card cage. It’s clearly straight through so should be fine.

160106-IMG_20160106_194705That means that I can get to the board with my meter and ‘scope etc. I have also removed the AVO (advanced Video Output) board and the small inter-connect board. This hasn’t changed the symptoms at all.

The first real diagnostic work was to measure the voltages from the PSU. They all seem fine.

I have been able to use a logic analyser (borrowed – I really want one of these) and I’ve been taking a look on the bus.

have attached three screen shots taken of the logic analyser screens. I have 18 channels and so I have the data bus, the lower 8 bits of the address bus and the synch pin. All signals are from clips on the 8080.

I have the triggers set to stable high on sync (start of new instruction) and 0 on the address bus. I put the analyser to wait for trigger and turned on the VT180.
The three shots are from the same run and I’ve just stepped through the time a little to show what happens at start up.

vt180-digiview-3vt180-digiview-2vt180-digiview-1I get this with or without the keyboard. With the keyboard, all of the lights are lit. When I first started on this repair, a few, normal looking lights came on first and then, after a while, they all came on. It’s a funny old world.

 

Retrochallenge 2016 – Setting up my stall.

On the eve of ‘challenge I have retrieved my VT-180 from the “shelf of good intentions”. I have taken photos of the two main boards and powered the machine up to see what happens.

151231-IMG_20151231_112224 151231-IMG_20151231_112314The first board basically the Z80 board. The second is a VT-100 terminal (if I remember correctly) and they talk to each other over the flat ribbon cable in the second photo.

Hmmm.

At the moment I don’t have the processor board in place as I think the VT side should come up without it. However, the current state of play is less than ideal.

151231-IMG_20151231_174248Roll on Tomorrow πŸ™‚

 

Retrochallenge 2016. Step forward VT-180.

7ed07f63f5e5d6b2074f8a85a85c287eI was given this VT-180 machine a few years ago and after a quick look, I put it on the shelf to get round to later.

Retrochallenge 2016/1 is the later it’s been waiting for.

My aim this January is to mend this rather under rated but rather splendid CP/M-80 machine and get it to live, breathe and jump again.

Quick, to the Bat Cave.

Retrochallenge 2016 – Decisions decisions.

Retrochallenge 2016 will soon be upon us. This month long chance to dust off old kit and play about a bit is always great fun and a chance to get round to stuff I’ve wanted to have a crack at for ages.

Tradition dictates that I try in all earnestness to achieve something but I don’t hit my target. I’m not sure that it matters.

So, what to go for this time around? I’m not too sure yet. I certainly have a number of loose ends to tie up. I also have a whole load of new threads to pick at.

I quite like the idea of getting a SCSI/SD card adapter working on my PDP-11. I’ve got as far as plugging it in. Could January be its month?

Last month I found out about DEC’s T11 chip. This was

"a microprocessor that implements the PDP-11 instruction set architecture (ISA) developed by Digital Equipment Corporation. The T-11 was code-named "Tiny". It was developed for embedded systems and was the first single-chip microprocessor developed by DEC."

I’ve found a few designs for systems that use it, including DEC’s own development board, and I rather like the idea of building a small single board computer based on that design. A bit like the designs that Grant Searle as published for other retro processors.

Also, I promised myself that I’d spend some time on the DEC Robin AKA VT-180 CP/M machine that’s been on the shelf of “good intentions” for a few years now.

Oh well, still a few of weeks to choose before kick-off on Jan the 1st.Β  Wish me luck.

 

 

RML380Z – Signs of life.

151014-IMG_20151014_213240378OK. Getting excited now πŸ™‚

I swapped the 4116 DRAMS from the CPU board with those on the RAM expansion card. And now… Ta Daa. I haven’t’ tried the RAM expansion card yet and so I don’t know if the chips are faulty or just dirty and re-seating them has done the trick but so far so bloody brilliant. I’ve waited 35 years for this.

πŸ™‚