• Please review our updated Terms and Rules here

Need a Terminator Pack for a TRS 80 Model II

Lorne

Veteran Member
Joined
Jul 27, 2008
Messages
1,164
Location
Chandler, AZ, USA
I'm in need of a terminator pack for a Model II.
Its the thing that plugs into the back of the Model II where the Expansion Box cable would go, so that you can boot from the Model II without the Expansion Box.
It would be a brown & black plastic thing approximately 4" long, 3/4" high, and 1 1/2" deep.

Does anyone have one they don't need or would otherwise be willing to part with?

I'll pay for it, trade something for it, whatever.
 

Druid6900

Veteran Member
Joined
May 7, 2006
Messages
3,809
Location
Hamilton, Ontario, Canada
Nope, Tandy choose to use an external terminating pack on the Model II so that you didn't have to keep taking the computer apart to use it with and then without the drive expansion bay (which does contain a terminated drive).

When adding drives to the expansion bay, one pulled the terminator dips from the first drive and stuck them in the added drive. Or if you were lazy, like me, because the pack was in a hard-to-reach location, you would just undo the four bolts holding the drive down, slide it over one position and mount the new (unterminated) drive in the first position.
 

Chuckster_in_Jax

Veteran Member
Joined
Feb 28, 2006
Messages
1,354
Location
Jacksonville, Florida
Nope, Tandy choose to use an external terminating pack on the Model II so that you didn't have to keep taking the computer apart to use it with and then without the drive expansion bay (which does contain a terminated drive).

When adding drives to the expansion bay, one pulled the terminator dips from the first drive and stuck them in the added drive. Or if you were lazy, like me, because the pack was in a hard-to-reach location, you would just undo the four bolts holding the drive down, slide it over one position and mount the new (unterminated) drive in the first position.

OK, so you're saying for someone who doesn't have an expansion bay, you could just open the main case and add the terminator dip to the internal drive and then you wouldn't need the external terminator? It makes sense to me.
 

NeXT

Veteran Member
Joined
Oct 22, 2008
Messages
6,952
Location
Kamloops, BC, Canada
I did not receive the terminator pack with my Model II and the system runs fine without a terminator, even when my expansion cabinet is not installed.
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,767
Location
Pacific Northwest, USA
Same here for my Model 16--the second floppy drive has the termination installed. If you're not going to use the system with an external floppy box, there's no point to the external terminator. In any case, it's just a few 150 ohm resistors between the floppy output lines to +5. Simple enough to make one, if you need it.
 

Lorne

Veteran Member
Joined
Jul 27, 2008
Messages
1,164
Location
Chandler, AZ, USA
Same here for my Model 16--the second floppy drive has the termination installed. If you're not going to use the system with an external floppy box, there's no point to the external terminator. In any case, it's just a few 150 ohm resistors between the floppy output lines to +5. Simple enough to make one, if you need it.

I think I do want to make one.
It wouldn't be for permanent use - I'd eventually like to have the Expansion Box connected, but meanwhile when I'm trying to work on the Model II, I have to have the Expansion Box sitting beside and connected to the Model II and that doesn't leave me any room on my workbench for anything else.

I'm looking at the signal pinouts/descriptions for the 50 pin cable and I don't see any +5 in that cable.
And which are the floppy output lines?
 

Chuckster_in_Jax

Veteran Member
Joined
Feb 28, 2006
Messages
1,354
Location
Jacksonville, Florida
I'm looking at the signal pinouts/descriptions for the 50 pin cable and I don't see any +5 in that cable.
And which are the floppy output lines?

Lorne,

Do you have the TRS-80 Model II Technical Reference Manual? That and the Shugart SA800-801 OEM and Users Manual should have the info you need. They should be available online. If you have trouble finding them let me know.
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,767
Location
Pacific Northwest, USA
I did a little homework and looked at the FDC schematics, which appear to show termination on the FDC board. There's also this:

At several places in the manuals it is stated that for operation without the Disk Station, a terminator has to be placed on the Disk Expansion connector to provide proper termination for signals to the drive. It is unclear to me how a passive terminator (no power available on the Disk Expansion connector) can power the neccesary pull-up resistors for the open collector outputs. I have no terminator and it works ok without Disk Station.

From Technical Bulletin II-019:

DISCUSSION/PROCEDURE: The Late Design FDC board is very different
from the early style FDC board. It incorporates the Western Digital 1691
Floppy Support Logic and the 2143 four phase clock chips. Variable
precompensation and a software reset are also used. Jumper options are
available for different modes of operation. when this board is installed
the external terminator plug is not used. Also, if an expansion bay is in
the system it does not have to be powered up to use the computer.

You may be chasing a mirage.
 

Lorne

Veteran Member
Joined
Jul 27, 2008
Messages
1,164
Location
Chandler, AZ, USA
You may be chasing a mirage.


Maybe not.

The FDC in my Model II doesn't appear to be the late design board.
After reading your post I wish it didn't, but mine does have a Western Digital FD1791B-02 chip on it which is what the schematics show in the manual.

Maybe that's why NeXt doesn't need the resistor pack. (NeXt: you wanna trade FDC cards?)
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,767
Location
Pacific Northwest, USA
Both versions of the FDC boards use the WD1791; the later board uses the WD1691 (20 pin DIP) and WD2143 (18 pin DIP) clock generator in addition, rather than a bunch of random logic. The two look like any other 20 pin/18 pin 0.300 DIP, so it's not obvious from a casual glance.
 

Lorne

Veteran Member
Joined
Jul 27, 2008
Messages
1,164
Location
Chandler, AZ, USA
Lorne,

Do you have the TRS-80 Model II Technical Reference Manual? That and the Shugart SA800-801 OEM and Users Manual should have the info you need. They should be available online. If you have trouble finding them let me know.

I have all those but unfortunately, that doesn't mean I always understand what I'm looking at.

(Side note: I haven't been able to find the Model II - Tech Ref online anywhere - if it's there, please let me know as I was thinking of scanning the whole thing so it can be available to others, and I won't bother if it's already there).

It gets screwy (for me anyway) in that the drive in the Model II is a Shugart SA-800, and the drive in the Disk Expansion Unit is a Magnetic Peripherals/Control Data 9404-B (info for which is also incl in the Tech Ref).
I'm not sure whether I'm supposed to be using the terminating info for the Shugart or the Control Data drive. The Disk Expansion Unit section of the Tech Ref refers me to the Control Data schematics for the termination stuff.

If it's a case of taking a 50 pin connector and soldering some resistors between certain pins, I can do that - I just can't figure out which pins the restistors should go between.

(PS: I've scanned the Floppy Disk Controller section of the manual (and it's schematics) if anyone needs them).
 

Lorne

Veteran Member
Joined
Jul 27, 2008
Messages
1,164
Location
Chandler, AZ, USA
Both versions of the FDC boards use the WD1791; the later board uses the WD1691 (20 pin DIP) and WD2143 (18 pin DIP) clock generator in addition, rather than a bunch of random logic. The two look like any other 20 pin/18 pin 0.300 DIP, so it's not obvious from a casual glance.


I'm not seeing those on my board:

FDC Board2.jpg

So as usual, and pretty much like everything else I seem to get, I've got the one I'd really rather not have ???
 

Kevin Adams

Member
Joined
Jul 4, 2010
Messages
35
The early disk controller required a Terminator connected to the external disk drive connector if no expansion chassis was connected.

I think this caused RS much grief as the "revised floppy disk controller" later released did not require the terminator.

I had to dig to find my notes on the wiring for the connector... here they are

Pin 4 connects to 40
Pin 6 connects to 38
pin 8 connects to 36
pin 10 connect to 34

Basically it loops signal lines back to terminator resistors on the internal disk drive. Without this "terminator", the disk drive chain would not be properly terminated.

Odd numbered connections are grounded so you can use a 7 pin flat cable to wire the loopback to a 50 pin connector. (see attached .jpg photo)

This loopback connector works fine on the one of my four model II's that uses the first generation floppy controller.

Kevin

I'm in need of a terminator pack for a Model II.
Its the thing that plugs into the back of the Model II where the Expansion Box cable would go, so that you can boot from the Model II without the Expansion Box.
It would be a brown & black plastic thing approximately 4" long, 3/4" high, and 1 1/2" deep.

Does anyone have one they don't need or would otherwise be willing to part with?

I'll pay for it, trade something for it, whatever.
 

Attachments

  • Model II Disk Loopback.jpg
    Model II Disk Loopback.jpg
    52 KB · Views: 2

Druid6900

Veteran Member
Joined
May 7, 2006
Messages
3,809
Location
Hamilton, Ontario, Canada
Yes, that's, basically, what the terminator pack did, they just fabricated a simple circuit board and put it in a nice little case. I think they were about 50 bucks if you lost yours....
 

Lorne

Veteran Member
Joined
Jul 27, 2008
Messages
1,164
Location
Chandler, AZ, USA
I had to dig to find my notes on the wiring for the connector... here they are

Pin 4 connects to 40
Pin 6 connects to 38
pin 8 connects to 36
pin 10 connect to 34

Basically it loops signal lines back to terminator resistors on the internal disk drive. Without this "terminator", the disk drive chain would not be properly terminated.

Odd numbered connections are grounded so you can use a 7 pin flat cable to wire the loopback to a 50 pin connector. (see attached .jpg photo)

This loopback connector works fine on the one of my four model II's that uses the first generation floppy controller.

Kevin

Perfect !

Thank you Kevin.
 

Chuckster_in_Jax

Veteran Member
Joined
Feb 28, 2006
Messages
1,354
Location
Jacksonville, Florida
(Side note: I haven't been able to find the Model II - Tech Ref online anywhere - if it's there, please let me know as I was thinking of scanning the whole thing so it can be available to others, and I won't bother if it's already there).

There are actually 2 Technical Manuals. One from 1980 and another from 1981. Also 2 Service manuals. They are in a TRS-80 Archive. What is the best site to submit these files so the community will have the best access to them.
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,767
Location
Pacific Northwest, USA
That terminator makes absolutely no sense. From the schematic, 4, 6, 8 are NC and 10 is the "2 sided" output from the drive. 40,38,36 and 34 are Write gate, Write Data, Step, and Direction.

If an internal drive has no termination packs, this will accomplish nothing. If the internal terminator is present, there's no need for this jumper setup.

Can anyone explain this one to me?
 

fjkraan

Experienced Member
Joined
Jul 30, 2003
Messages
118
Location
Netherlands
That terminator makes absolutely no sense. From the schematic, 4, 6, 8 are NC and 10 is the "2 sided" output from the drive. 40,38,36 and 34 are Write gate, Write Data, Step, and Direction.

If an internal drive has no termination packs, this will accomplish nothing. If the internal terminator is present, there's no need for this jumper setup.

Can anyone explain this one to me?

I had the same issue when I thought I needed the terminator. Having no info then, I concluded that it could only be some kind of loopback. But the schematics didn't provide any clue which pins should be connected. But I'm glad someone provided the info even if it makes no sense, other than as another Tandy money source.

What is the best site to submit these files so the community will have the best access to them.

I wasn't aware of the 1981 version, but the 1980 version is at http://electrickery.xs4all.nl/comp/trs80m2/doc/ or http://www.vintagecomputer.net/fjkraan/comp/trs80m2/doc/.
There is no official successor of the trs-80 archives, but I would be happy to host it.
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,767
Location
Pacific Northwest, USA
Lorne has pointed out to me that the earlier termination scheme with the jumper block relies on a peculiar wirewrap patch to the SA800, wiring the "user I/O" pins to spare terminator header pins. In other words, a terrible kludge...
 
Top