Model I with DIN Expansion Interface

[Fooser]

Greetings all.

I posted this thread in Yahoo Groups but it has stalled. I'm hoping
to get a little more feed back so I'm re-posting here. Sorry for the
duplication.

I'm in the process of building a Model I disk system using components
from different acquisitions. Both the CPU and Expansion Interface
have the DIN dongle, and I have a buffered CPU to EI cable.

When I plug in just the CPU and monitor, I get 15k from the ?mem
command. When I add the EI, I get the garbage screen. When I hold the
break key and press reset, same garbage screen. If I'm not mistaken,
holding down the break during reset should show the memory size screen
and a ?mem should show the additional EI memory. It does not... just
garbage.

I've replaced the two banks of memory on the EI several times thinking
it was a memory issue... no difference. I have two buffered EI cables
and have tried both. I have also swapped out the power supplies.

To help troubleshoot, I purchased a DIN dongled EI motherboard from
eBay and have exactly the same issue.

I have two other working Model I disk systems but have not actually
attached drive 0 since the memory on the EI is not being recognized.

I do turn on the EI before the CPU. Any suggestions what to check
next? I wish I could test the memory outside of the TRS-80 but I'm
not aware of a method. I guess I could take the memory from on of the
other working EI's but I hate to mess with a working system. :-)

Thanks folks.

Regards,
Don Mankin

[Mike Y]

"Fooser" <don.m...@gmail.com> wrote in message
news:95d3d031-cd9c-40ae...@x16g2000prd.googlegroups.com...

Make sure power is good on the EI. I'd pull all memory out of it and see if
I could get a boot first without any additional memory.

The DIN cables took across RAS, MUX, and CAS. But ONLY on the OLD EI, not
the EI with the DDU chip. That version of the EI regenerated the signals to
the RAM.

Make sure you have power getting to the buffered EI. I forget the pin, but
it should be at the end of the connector.

If I remember correctly, when the CPU sees the EI, it tries to boot from it.
When you see the garbage, you're seeing whatever happens to be there while
the system tries to reset and read from the FDC. Holding down the break key
should tell the CPU to ignore the FDC boot and continue on without disk.
Hmm, try the CPU with the buffered cable attached but NOT the EI. Without
the EI providing power to the buffered cable I think you should see the same
hang.

[Thierry_S]

Hi,

imvho, you should:

- First if it's not done already check the condition of the edge
connector on the CPU for oxidation, it's a common cause of failure on
the mod. 1

Anyway, being given that:

> If I'm not mistaken,
>> holding down the break during reset should show the memory size screen
>> and a ?mem should show the additional EI memory. It does not... just
>> garbage.

it mean always in my vho that the EI don't handle / release the data bus
of the CPU correctly.

If there is no oxidation problem you should check the CPU and EI to
ensure that it has the correct mods for the type of DIN dongle you have
as it seems that many quite different versions exist...

You can find some additional information about the various versions
produced here if you haven't found this already:

http://www.freak-search.com/en/thread/885384/to_buffer_or_not_to_buffer_that_is_the_question

My model 1(I bought it in 1981) is of the last series using the strong
ribbon wire. Absolutely never been faced to a failure in the cpu to EI
connection except for oxidation.


Hope this helps!

[Knut]

Response to a slightly old post but.

Before the screen clear the ROM looks for the floppy controller. It will write
to it and read back status. If the response is not sensible it assumes there is
no floppy interface and continues to boot ROM BASIC. Holding down the BREAK key
will make the initiation to skip this test. If the response is ok it will try to
read sector 0 of track 0 on drive 0. If that fails it will hang "forever". So
typically with the EI attached and no disk in the drive (or drive not attached)
you will get a screen of garbage and no response. Then you can attach a drive,
insert a boot disk or hold down break and press reset.

If ROM BASIC starts and no response is given to "MEM SIZE?" question it will
check RAM from 434Ch and up, byte by byte until the RAM doesn't work. The result
is used for HIGH$. This means that any gap or a failing byte will limit the
memory available to basic. So it is important that if you only have 16K in the
EI it has to go in the correct bank.

If the EI is modified for the buffer mod a straight cable must not be used.
There is normally a sticker on the EI telling you that you need the buffered
cable on such an EI.

A buffered cable does not work if the EI is not modified for it.

I have a web page about the EI at http://home.online.no/~kr-lund/m1ei.htm if you
look at the image where the buffered cable is there is an orange lead which
supplies 5V for the buffer mod. If a straight cable is used with this EI this 5V
will go to a ground pin on the model-I. Similarly you can't use the buffered
cable with an unmodified EI because the 5V is missing.

Note also that some older EI's works well without the buffer mod. I have one
like that. The other old EI has the buffer mod and I just assume it needed it.

Knut