VAX 11/730 quickie

[tony duell]

> >
> > I have found that those little in-line RS232 testers with 7 or so bicolour
> > LEDs monitoring the important signals are very useful when working on
> > a machine with a serial terminal. If you get flickering on the TxD or RxD
> > LEDs then it is sending something.
> 
> Yes and I usually use such; I have an assortment of things from inline
> testers to breakout boxes to Tektronic analysers. But this hookup was

So do I. I have been lucky a couple of times when people have decided that
nobody uses RS232 any more and have given me various nice bits of test gear,

The thing about the LED tester is that it doesn't need configuring, there are no
switches that could be set wrongly (or open, as on a breakout box), etc. So it 
does no harm [1]. I generally stick it in the link by default if I am bringing up a 
new machine ro similar.

[1] One day I will find a serial port with weak drivers that can't drive the LEDs and
still have enough voltage swing to operate the receiver properly. Such a port 
probably needs repairing anyway.

> so simple and obvious nothing could go wrong.... (!)

One of the laws of research is 'In any collection of data, that figure which is 
obviously correct, beyond all need of checking, is the mistake' :-). It applies 
to hardware too (as I have found out the hard way more times than I care
to remember!).


[...]

> > There should be a pause between the 'CONV0' and the '11' IIRC
> 
> Indeed that's how it comes up. Very short pause since I have most of
> the memory out as part of potential gotcha elimination - and the last
> two tests are memory tests IIRC; they take a little longer.

It's not testing the VAX memory, it's testing the console processor RAM and
I think the CPU control store RAM. 

> > You should then get 2 lines of read errors for DD1 and DD0 in that
> > order. If you get a 'Device Error' then the TU58 controller is not
> > responding at all, either it is not plugged in or it has serious problems.
> 
> Yep that was shown in the link I gave. In text it's:
> 
> CONV011
> ?27  READ ERROR DD1
> ?27  READ ERROR DD0
> ROM>^C
> 
> ?27  READ ERROR DD1
> ?27  READ ERROR DD0
> ROM>

Looks like the 8085 side is working correctly. That's what mine does.

> > I have 2 genuine 11/730 console tapes. Not that it does me any good, they
> > both have dropouts and are shedding oxide. The output of the read amplifier
> > in the TU58 is 'interesting' shall we say.
> >
> > I am currently rebulding a standalone TU58. My aim is to somehow find a good
> > tape (the hard part) and then to dump an 11/730 console tape image to it. That
> > means writing some kind of program to talk to the TU58 (another hard part).

> I did wonder how one might go about writing a tape image to a physical
> tape... I'm happy to get the thing loaded via the emulator for now -
> but I'd like to get real working tapes eventually.

Given that some of the TU58 emulators seem to need a PC or similar to run 
them, I am certainly not going to go that route! Modifying the TU58 firmware
to let it access some kind of flash device or possibly making a micorcontroller
board is a last resort if I can't get any tapes to work.

> 
> If it helps your 'hard part' I have at least a couple of brand new
> TU58 tapes - still sealed in plastic wrap...

Alas that doesn't mean much. I unwrapped a tape like that, it was the only
time I've had a belt break. The tape seems to fail with age and shed oxide.

The tapes are of course pre-formatted, but it may be possible to make a 
formatter for totally blank tapes. At least the format is documented, and it 
doesn't involve anything that can't be written by a normal head.

-tony