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Need a Terminator Pack for a TRS 80 Model II

And to top it all off, I've got two Shugart 801's.
Only one of them has the PCB that would allow those wire wrap jumpers to be installed per their diagram.
So, if you've got one of the different 801's or even an 800-2 you'd be screwed, because the PCB on the drive is different.
I think kludge is the correct term.
 
Need to correct this. Only 1 Technical manual from 1980 and 1 Service Manual.

Good - the 1980 one is what I've got.
Glad I don't have to scan the thing.

In case anyone is interested in it, in the same package I also got:

ScripsitSpelling and Hyphenation Dictionary
Manual

Model II Scripsit 2.0
Reference manual

Profile II Training Course
Manual
Disk: Profile II
Disk: Profile Plus
6 cassette training tapes

Profile Plus System upgrade
Manual
Disk: Profile Plus System Upgrade

Technical Reference Handbook
Manual

Profile II
Manual

Owner’s Manual
Manual

Profile Prosort
Manual
Disk: Profile Prosort

Model II Scripsit 2.0
Manual
4 cassette training tapes
 
So, if you've got one of the different 801's or even an 800-2 you'd be screwed, because the PCB on the drive is different

Both the 800 and 801 have access to the "user pins", just no spare terminator points. So add your own 150 ohm resistors between the user pins and +5 and you've got it.
 
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...

Possibly, but, would you want to have to take your computer apart every time you wanted to use your second drive?

Given the logistics, it was a fairly elegant solution.

It was the same with external hard drives. The case was built with a little round port-hole that you could unscrew to remove the terminating resistor DIP when you added a 2nd, 3rd or 4th drive to the chain and plug it into the new "last" drive. Sure beats having to take the case off, pull the bubble, flip it over and pull the resistor pack then close it all up and repeat it with the second drive.
 
Since we're talking about termination here, make sure that with the drive not being accessed, STEP, DIR,WGATE, WDATA all read high (>4 volts). You could simply have the termination messed up. Try the "regular" termination (T3, T4, T5, T6 jumpers installed) if you have doubts.
 
Here are some notes I made from a news group posting and a website Chuck mentioned:
Here is the pinout (from http://fjkraan.home.xs4all.nl/comp/trs80m2/fixing.html)

These lines were terminated in the Disk Station, on the last drive in the cable (as it should):

TRS-80 MODEL II floppy drive terminator
Code:
50p.  func.   terminator pin
---+------+---+--------
 2 | NC   | > |  7   Low current
 4 | NC   |   |
 6 | NC   |   |
 8 | NC   |   |
10 |      | < |      Two sided
12 |      | < |      Disk change
14 | SDSEL| > |      Side select
16 | NC   |   |
18 | HLD* | < |      Head load
20 | IP*  | < |      Index pulse
22 | RDY  | < |      Ready
24 | NC   |   |
26 | DS1* | > | 11   Drive select 1
28 | DS2* | > | 12   Drive select 2
30 | DS3* | > | 14   Drive select 3
32 | DS4* | > |  2   Drive select 4
34 | DIR* | > |  1   Direction select
36 | STEP*| > | 13   Step
38 | CPWD*| > | 15   Write data
40 | WG*  | > | 10   Write gate
42 | TRK0*| < |      Track 0
44 | WPRT*| < |      Write protect
46 | RD*  | < |      Read data
48 | NC   |   |
50 | NC   |   |
These are all the signals from the disk controller to the disks. The signals to the disk controller are terminated on the disk controller board. All signals are open collector, meaning the high level is provided by the terminator, which is basically a resistor to Vcc. The low level is provided by the collector of a transistor switched on. The advantage is that multiple devices (read disk drives) can control the line.
The terminator in the Disk Station was more advanced, probaly to dampen reflections due to the long flatcable; 215 cm (or 85 inch). BTW, there is also a short cable to the internal drive;
Code:
   +5V
    |
   +++
   | |
   | | 220 ohm
   | |
   +++
    |
    +--- signal
    |
   +++
   | |
   | | 330 ohm
   | |
   +++
    |
   GND
YMMV
 
Since we're talking about termination here, make sure that with the drive not being accessed, STEP, DIR,WGATE, WDATA all read high (>4 volts). You could simply have the termination messed up. Try the "regular" termination (T3, T4, T5, T6 jumpers installed) if you have doubts.

With the ribbon cable not connected to the drive:
WGATE (pin40) = low
WDATA (pin38) = low
STEP (pin 36) = nothing
DIR (pin 34) = nothing
(It doesn’t matter if the terminator is installed or not – the readings are the same).



With the ribbon cable connecting the drive to the drive controller:
WGATE (pin 40) = low
WDATA (pin38) = nothing
STEP (pin 36) = nothing
DIR (pin 34) = low
(It doesn’t matter if the terminator is installed or not, and doesn’t matter if there’s a disk inserted or not – the readings are the same).

If they're all supposed to be high, I guess I have doubts, so I better try it with T3-T6 jumpered instead.
 
Hmmmm.....with T3 to T6 jumpered (instead of the wire wrap jumpers), I get:

With the ribbon cable not connected to the drive:
WGATE (pin 40) = high

WDATA (pin38 ) = low

STEP (pin 36) = high
DIR (pin 34) = high

I think I'm going to check my readings with the wire wrap jumpers in place.
 
BTW, there is also a short cable to the internal drive;

There is a difference between the early FDC cards and the later:
* the early ones had essentially one long flatcable from FDC card - internal floppy - external connector - external floppy drives
* the later ones had two connectors, one to the internal floppy and one to the external connector and floppy drives.

Only the early configurations needed the loopback/terminator. This is all described in the M2 technical bulletins :
http://electrickery.xs4all.nl/comp/trs80m2/doc/Model_II_Technical_Bulletins.pdf or
http://www.vintagecomputer.net/fjkraan/comp/trs80m2/doc/Model_II_Technical_Bulletins.pdf

Maybe one day I'll make a visual catalog of all the cards I have :)
 
There is a difference between the early FDC cards and the later:
* the early ones had essentially one long flatcable from FDC card - internal floppy - external connector - external floppy drives
* the later ones had two connectors, one to the internal floppy and one to the external connector and floppy drives.

Only the early configurations needed the loopback/terminator. This is all described in the M2 technical bulletins :
http://electrickery.xs4all.nl/comp/trs80m2/doc/Model_II_Technical_Bulletins.pdf or
http://www.vintagecomputer.net/fjkraan/comp/trs80m2/doc/Model_II_Technical_Bulletins.pdf

Maybe one day I'll make a visual catalog of all the cards I have :)

Yeouch - there's some reading to be done here, and some stuff to check - this'll keep me busy for a bit.
Thanks for these bulletins.
 
Here are some notes I made from a news group posting and a website Chuck mentioned:
Here is the pinout (from http://fjkraan.home.xs4all.nl/comp/trs80m2/fixing.html)

These lines were terminated in the Disk Station, on the last drive in the cable (as it should):

TRS-80 MODEL II floppy drive terminator
Code:
50p.  func.   terminator pin
---+------+---+--------
 2 | NC   | > |  7   Low current
 4 | NC   |   |
 6 | NC   |   |
 8 | NC   |   |
10 |      | < |      Two sided
12 |      | < |      Disk change
14 | SDSEL| > |      Side select
16 | NC   |   |
18 | HLD* | < |      Head load
20 | IP*  | < |      Index pulse
22 | RDY  | < |      Ready
24 | NC   |   |
26 | DS1* | > | 11   Drive select 1
28 | DS2* | > | 12   Drive select 2
30 | DS3* | > | 14   Drive select 3
32 | DS4* | > |  2   Drive select 4
34 | DIR* | > |  1   Direction select
36 | STEP*| > | 13   Step
38 | CPWD*| > | 15   Write data
40 | WG*  | > | 10   Write gate
42 | TRK0*| < |      Track 0
44 | WPRT*| < |      Write protect
46 | RD*  | < |      Read data
48 | NC   |   |
50 | NC   |   |
These are all the signals from the disk controller to the disks. The signals to the disk controller are terminated on the disk controller board. All signals are open collector, meaning the high level is provided by the terminator, which is basically a resistor to Vcc. The low level is provided by the collector of a transistor switched on. The advantage is that multiple devices (read disk drives) can control the line.
The terminator in the Disk Station was more advanced, probaly to dampen reflections due to the long flatcable; 215 cm (or 85 inch). BTW, there is also a short cable to the internal drive;
Code:
   +5V
    |
   +++
   | |
   | | 220 ohm
   | |
   +++
    |
    +--- signal
    |
   +++
   | |
   | | 330 ohm
   | |
   +++
    |
   GND
YMMV

I'm getting confused.

Technical Bulletin No II:001 indicates that four wire wrap jumpers are to be installed on the internal Drive 0 (if it is a Shugart), and if not using an expansion bay then an external terminator must be plugged into the expansion bay connector on the back of the Model II (but only when using the early design FDC), and Technical Bulletin No II:030 indicates that the wire wrap jumpers are required on the internal Shugart drive logic board (but again, only when using the early style FDC).
Is this post suggesting that the terminator to be plugged in the back of the Model II should have the same termination as the disk station?

"These are all the signals from the disk controller to the disks. The signals to the disk controller are terminated on the disk controller board."
If they are being terminated on the disk controller board, why would they neeed to be terminated at the back of the Model II ?
Could it be that the disk controller board being mentioned, is the later design board which didn't need an external terminator plugged into the back of the Model II ?
 
Quick answer:

There are two types of signals in a floppy hookup. Host-to-drive and Drive-to-host. Both are of the open-collector variety. In other words, the line is pulled high through a resistance (in the case of an SA800-type interface, about 150 ohms) and, if it's host-to-drive, the host pulls the line low to signal. If it's drive-to-host, the drive pulls the line low. Ideally, you want the termination resistance at the opposite end of whatever is doing the pulling to reduce line reflections.

This system has a couple of interesting attributes, where you can have multiple controllers as well as multiple drives on a single ribbon cable.

However, you have to remember that when this system was devised, floppy drives were very often at the end of long cables (>1m) as compact LSI-based disk controllers didn't exist. Logic was plain 7400 TTL; not even Schottky-clamped. In essence, we're talking about a 1969 design.

In point of fact, if the floppy drives are sharing the same box as the controller, it doesn't matter where the pullup/terminator is located. Logic families are better and cables are shorter.

In late floppy drives, the termination resistance is in the neighborhood of 2.2K, and drivers are usually 3-state instead of open collector. The very high pullup is why there's no option to select termination on 3.5" drives--it simply doesn't matter for any recent application.

So, I'll say this again. Forget about the wirewrap jumpers on the drive. Use the Shugart-provided terminators T3-T6. If you decide to add an external drive box, just remember to remove the terminator jumpers on the internal drive. It won't hurt if you forget, BTW.
 
Lorne,

I don' think your measurements are going to be valid until you actually get the drive to boot as we aren't sure where the problem lies.

I'd just keep using the Drive Bay to terminate the system until it actually boots and THEN worry about getting/building a terminator for the Model II so you can run it without the Drive Bay, if you want.
 
Lorne,

I'd just keep using the Drive Bay to terminate the system until it actually boots and THEN worry about getting/building a terminator for the Model II so you can run it without the Drive Bay, if you want.

I've just been trying to understand what the terminator actually does, and after drawing a couple little diagrams, I think I've got it now.
The external terminator does exactly the same thing as using jumpers on T3, 4, 5 & 6 does - it just does it in a convoluted way (ie: four wire wrap jumpers and an external terminator instead of four little jumpers).
I get it now, but I just can't help shaking my head about it.
 
I've just been trying to understand what the terminator actually does, and after drawing a couple little diagrams, I think I've got it now.
The external terminator does exactly the same thing as using jumpers on T3, 4, 5 & 6 does - it just does it in a convoluted way (ie: four wire wrap jumpers and an external terminator instead of four little jumpers).
I get it now, but I just can't help shaking my head about it.

Well, as I said, they couldn't very well do it any other way.

Could you picture some ham-handed businessman opening up the model two and removing the termination jumpers so he could use the new Drive Expansion Bay he just bought?

Much easier to have a little plug-in to remove and just plug the cable from the expansion box in.

And, if he wanted to take just the computer (since a loaded Drive Expansion weighed, oh, about 60 pounds) to another location, instead of opening it up again, re-terminating it and then having to unterminate it to hook it back up to the expansion bay, just plug and unplug as needed.
 
Just to illustrate how the contraption on the SA800/801 drive looks, I made an image. The two blue-ish connectors connect the terminator side of T3, T4, T5 and T6 with floppy drive connector pin 4, 6, 8 and 10. The 'terminator'-plug on the external connector connects these pins to external connector pins 34, 36, 38 and 40. The combination of these two modifications have the same result as putting jumpers on T3, T4, T5, T6. With the additional advantage that it allowed enabling and disabling of termination without opening the case.
Not only the Shugart SA800/801 had this option, I also saw a similar contraption on a variant of the Control Data / Magnetic Peripherials 9404 floppy drive which was also used in the Model II.
 

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