System 80 4020 expansion unit issues

[Nama]

I pulled my System 80 out of it's box yesterday.
I wanted to test an Ohio Scientific drive with another machine and the
System 80 is the only computer I have that uses a 5.25" floppy
connector.
Unfortunately when the System 80 is attached to the expansion unit and
the unit is turned on, all I get is a screen full of seemingly random
characters (although fairly consistent pattern on consecutive power
ups):

Otherwise the System 80 seems to function ok without the expansion
unit being attached. And even with the unit attached I can 'Break'
'Reset' to the ready prompt from the corrupt screen.

I have checked the continuity on the ribbon cable from the System 80
to the expansion unit and it all looks ok. I also changed the
orientation of this cable around and that didn't help either.

I'm using a Canon 5.25" drive (not the OSI one yet) as I know when the
System 80 is working this drive plays well with it.

Doing a "?MEM" shows 31956k RAM (not 32896k which is full 32k) without
the expansion unit attached, and 48340k with the unit attached. Not
sure if that is right or important at all.

Hoping someone here may be able to point me in the right direction for
testing.

Cheers
Phil

[Leslie Ayling]

Hi Phil,

>I pulled my System 80 out of it's box yesterday.
>I wanted to test an Ohio Scientific drive with another machine and the
>System 80 is the only computer I have that uses a 5.25" floppy
>connector.

OSI drives use a proprietary interface, which isn't shugart compatible!
Check here:
http://192.197.62.35/staff/mcsele/OhioScientific.html
for more info on everything OSI :)

>Doing a "?MEM" shows 31956k RAM (not 32896k which is full 32k) without
>the expansion unit attached, and 48340k with the unit attached. Not
>sure if that is right or important at all.

Have you used this 4020 interface with this particular System-80 before?

Sounds like the Sys-80 has a 32K in keyboard mod which may be conflicting
with expansion RAM in the 4020 interface.

Cheers,
Leslie

[Terry Stewart]

Good thoughts Leslie, but Phil has an expansion unit (from me) which was modified to take into account the 32K keyboard mod.

Phil can <BREAK><RESET> with the IE attached and get the right amount of memory.  I've just asked him privately to post more details particulary if the unit tries to access drives when RESET is pressed.  It could be disk, disk cables, drive, or the floppy interface if a known good disk and good drive fails to clear the garbage screen yes?

31954 is the normal RAM shown for a 32 K unit as is 48338 for a normal 48k. The RAM seems fine.

Terry

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[Terry Stewart]

In saying that, Phil's RAM seems to have two extra bytes from somewhere, at least compared to that I'm seeing on Matt's emulator.  Whether this is significant or not I don't know.

Terry

[Leslie Ayling]

Hi Terry,

 

31956 and 48340 (32K and 48K respectively) are the free memory when using the original

“MEMORY SIZE?” Level 2 ROM, or original System-80 for that matter.

 

The later “MEM SIZE?” ROMS have 2 bytes less free: 31954 and 48338.

 

Cheers,

Leslie

[Terry Stewart]

To answer my own question, the extra two bytes is the difference between a System 80 ROM and a TRS-80 one.  That RAM is completely correct Phil

Terry

[Terry Stewart]

Yes, that is indeed the case.  Cheers

Terry

--

[Nama]

Hi guys,
thanks for the replies and confirmation that RAM is working.
I have been playing with it today and I can't seem to make any
progress. I tested all the cables and they all seem to have good
continuity, although sometimes if I plug in the expansion cable it may
only show 32k, refitting or flipping the cable will often bring it
back to 48k.

I've tried many floppy disks (the ones Terry made for me) and even 2
disk drives now (a Shugart SA400 and a cannon half hight drive).
Basically the drive head doesn't move so it doesn't look like it's
seeking. The disk green light on the Canon drive will dim for about 4
seconds and then come bright again. The Canon drive spins continuously
as I believe this is what it is designed to do. With the Sugart drive
it would spin up for about 4 seconds then stop. Heads don't seem to
move either. So it seems like both drives basically do the same thing.

> OSI drives use a proprietary interface, which isn't shugart compatible!
> Check here:http://192.197.62.35/staff/mcsele/OhioScientific.html
> for more info on everything OSI :)

Yes, I realize that the OSI drives are different, but only in that
that have a data separator built on a separate small circuit board
that plugs into the main floppy board. Otherwise I believe it's just a
standard MPI 51 drive, and I know Dick Smith used these drives for the
System 80 because Terry has a few. I was going to unplug the small
circuit board before testing the OSI unit.

Cheers

Phil

[Nama]

Just had a look with my logic probe to see what the READ_DATA line was
doing from the drive when reset was pressed. Sure enough it started
pulsing and that pulsing lasts about 4 seconds. I followed this line
to where I believe it eventually arrives at the FD1771 as F.D.DATA
line on pin 27. On reset this pulses low , again for about 4 second
and returns to a solid low signal after. Now I may be completely wrong
here, but I would expect the data lines (0 thru 7) on the FD1771 to
pulse too when reset is pressed, but they don't seem to do what I
would expect.
DAL0 starts by pulsing low until reset is pressed and the signal seems
to disappear for about a second before returning to it's original
state.
DAL1 thru DAl7 are all high until reset is pressed and the signal
seems to disappear for about a second before returning to it's high
state.

Is this what would be expected?

[Leslie Ayling]

Hi Phil, et al.

Fact that you can see the drive select light come on for 4 seconds is a good
sign.
Boot routine in the ROM can "see" the FD Controller in the expansion unit.
Means most of the select logic is functioning normally.

If you have a logic probe I would start looking for negative going pulses
on the /STEP signal (pin20) *at the drive* end right after you hit the reset
button.

If nothing is there, try looking at the output of Z36 pin 2 (also the /STEP
signal).
If still nothing, try replacing Z36 (a 7416 open collector inverting
driver).

The 7416 may be a little difficult to find, you can safely use a 7406
instead.

7406 is rated at 30V compared to the 15V of the 7416.

------
Also worth checking the drive select lines on pins 10,12,14,32 during a
reset.
If missing, replace Z40 (also a 7416 driver).

See how you go with that.

Cheers,
Leslie

-----Original Message-----
From: eaca-di...@googlegroups.com
[mailto:eaca-di...@googlegroups.com] On Behalf Of Nama
Sent: Sunday, 29 January 2012 10:13 PM
To: Eaca discussion
Subject: Re: System 80 4020 expansion unit issues

[Nama]

Thanks for the feedback.

The /STEP signal (pin20) of the drive is high, and when reset is
pushed it pulses high for 4 seconds.

The output of Z36 pin 2 does the same as above.

Pin 10 is high then goes low for 4 seconds and returns high
Pin 12 and 14, no signal readable on probe
Pin 32 is high with no change on reset.

Cheers again
Phil

[Leslie Ayling]

Hi Phil,

I assume you are performing your tests with a formatted diskette in the
drive?

What you see on the FD Data pin sounds correct.
If you want to try it with the external data separator disabled, remove J3
and J4 and
switch J1 such that PIN2 of Z58 feeds into FD Data on pin27 of the 1771.

That will isolate quite a bit of circuitry.

As the DAL bus is inverted, I would expect all pins to be high impedance
when the
1771 isn't selected. There aren't any pull-up/pull-down resistors between
the
FDC and the LS368 bus drivers (Z38/Z39), so they could float anywhere...

Leslie

-----Original Message-----
From: eaca-di...@googlegroups.com
[mailto:eaca-di...@googlegroups.com] On Behalf Of Nama
Sent: Monday, 30 January 2012 12:14 AM
To: Eaca discussion
Subject: Re: System 80 4020 expansion unit issues

[Leslie Ayling]

Hi Phil,

>The /STEP signal (pin20) of the drive is high, and when reset is
>pushed it pulses high for 4 seconds.
>The output of Z36 pin 2 does the same as above.

>Pin 10 is high then goes low for 4 seconds and returns high

Drive zero is being selected ok, and is receiving the step pulses.

How about direction select? Pin 18 (Z36 pin4).

Good luck, off to bed for now.

ZZZZzzzz....
Leslie

[Nama]

> I assume you are performing your tests with a formatted diskette in the
> drive?

Errr, actually I'm using an unformatted disk for these tests as I
don't want to accidentally wipe one of my good disks.
I did however check the FD data line once with a formatted disk and it
basically seemed to do the same as with my unformatted disk. Should I
use a System 80 formatted disk?

> If you want to try it with the external data separator disabled, remove J3
> and J4 and
> switch J1 such that PIN2 of Z58 feeds into FD Data on pin27 of the 1771.

Sorry, I'm not quite following. Will this basically disable the data
separator circuit in the expansion board?
I was thinking once the expansion board is working again (hopefully).
I would test the MPI51 drive by removing the small data splitter in
the drive itself. Maybe this isn't a good idea. Not sure. Do I also
need to duo the mod you mentioned too?

Cheers

[Nama]

> How about direction select? Pin 18 (Z36 pin4).

Pin 18 is high, and says high on reset.

Thanks for your help and good night.

Phll

[Nama]

> Fact that you can see the drive select light come on for 4 seconds is a good sign.

Well, let me just confirm this. The drive light is actually always on
(green), but dims during the 4 second period when the READ_DATA line
is pulsing.

[Terry Stewart]

Phil, I'm not quite following.  Wouldn't you need to do this with a formatted, DOS disk?  From memory most other things will leave you just with garbage screen?

I'll be offf the scene for a few days.  Just going on leave to a place where Internet might be scarce.  Good luck with things.

Terry

[Knut]

Hi

I think you need to test with a known good disk. And if you haven't already
booted a DOS it needs to be a bootable DOS disk. The M1/Sys80 ROM only knows how
to read sector 0 side 0 track 0 in single density. After a successful read of
this sector it will pass control to this program. This ROM code is very simple
and assumes everything to work. So any problem and it will hang with an
uninitiated screen. The floppycontroller will respond with error status to
report problems but the ROM doesn't look for these.

Use writeprotection for any disk you don't want to destroy. 5.25": tape the
notch in the side of the disk, usually needs to be sturdy enough for mechanical
detection. Don't power on or off with a diskette in the drive.

It might actually be easier to debug a drive if it is not the boot drive. The
boot process relies on old and simple code in the ROM. The DOS drivers will be
much better and you will get errormessages based on what the floppycontroller
has problems with. For example CRC error... which BTW is enough to stop the boot
process.

Leslie mentioned that Ohio Scientific drives are not shugart compatible.
M1/Sys80 can only use shugart compatible drives. Is the Ohio Scientific drive
you have meant for use with an Ohio Scientific computer? What computer was it
used with?

Knut :-)

[Nama]

> Phil, I'm not quite following.  Wouldn't you need to do this with a
> formatted, DOS disk?  From memory most other things will leave you just
> with garbage screen?

Yes, I've tried booting with multiple different NewDOS formatted disks
(the ones you made for me Terry) but the screen is always garbage and
the computer never sees a DOS. I thought using a blank floppy would
surface while I am just poking around with the probe, as the drive
seems to do exactly the same thing regardless of what disk is
installed. Once an issue was found I would fix and try again with a
DOS disk.
I'll use a formatted disk if you guys thing it's important at this
stage.

To answer Knut's question, The drive is an MPI 51 that comes with and
OSI C4. As far as I know the drive is stock with the addition on a
small plug in daughterboard that acts as a data splitter, which the
OSI machine needs. I believe that removing this will make it Shugart
compliant.

Cheers
Phil

[Nama]

I spent some time today testing the continuity on both the floppy and
the expansion cables. Although I can not be 100% certain, it does seem
like these are making good connections.

If anyone has any ideas where I should look next I would greatly
appreciate it.
If it helps, I have also dragged my old O-scope out of the closet.
Although I am purely a novice with it, if I knew where to look, I am
capable of taking basic readings and relaying the findings.

Thanks again.
Phil

[Leslie Ayling]

Hi Phil,

>> I assume you are performing your tests with a formatted diskette in the
>> drive?

>Errr, actually I'm using an unformatted disk for these tests as I
>don't want to accidentally wipe one of my good disks.
>I did however check the FD data line once with a formatted disk and it
>basically seemed to do the same as with my unformatted disk. Should I
>use a System 80 formatted disk?

Yes, else any test results will be meaningless.
ROM routines will execute, even if the FDC works it won't find any sector
info
and will hang about 4 seconds later.

>> If you want to try it with the external data separator disabled, remove
J3
>> and J4 and
>> switch J1 such that PIN2 of Z58 feeds into FD Data on pin27 of the 1771.

>Sorry, I'm not quite following. Will this basically disable the data
>separator circuit in the expansion board?

Yes, temporarily.
If it were to work with the data separator circuit disabled, it may help
you pinpoint what is working/not working.

>I was thinking once the expansion board is working again (hopefully).
>I would test the MPI51 drive by removing the small data splitter in
>the drive itself. Maybe this isn't a good idea. Not sure. Do I also
>need to duo the mod you mentioned too?

OSI drives are *not* going to work with the X4020. It isn't a simple matter
of removing the data separator.
Look at page 74 of the OSI C4P service manual:
http://www.osiweb.org/osiweb/manuals/SAMS-C4P-Service-Manual.pdf
which specifically deals with the 505 CPU board including disk controller.

There are several signals which don't appear on a Shugart compatible drive.

It's not too difficult to bodgey a normal shugart drive to work in an OSI
system as ready-only, but the reverse can't necessarily be said :(

Leslie

[Leslie Ayling]

This is not sorrect.

Sounds like drive may be faulty/jumpered incorrectly.

Light should be off normally, then light for approx 4 seconds after a reset.
(assuming no disk in the drive from which to boot).

Cheers,
Leslie

-----Original Message-----
From: eaca-di...@googlegroups.com
[mailto:eaca-di...@googlegroups.com] On Behalf Of Nama
Sent: Monday, 30 January 2012 1:23 AM
To: Eaca discussion
Subject: Re: System 80 4020 expansion unit issues

--

[Leslie Ayling]

Hi again Phil,

>Yes, I've tried booting with multiple different NewDOS formatted disks
>(the ones you made for me Terry) but the screen is always garbage and
>the computer never sees a DOS.

The read data appearing at the FDC is certainly fluctuating during
the reset procedure.

Data separator circuit in the X4020 is made of 3 one-shot's which
use simple R/C networks to determine their timing/duration etc.
It's possible that with age, the timing parameters have gone out
of spec.
Disabling the data separator may isolate that as a cause of it not
working correctly.

Temporarily disabling the data separator in the X4020 may help
to get it working, at least temporarily.

Leslie

[Nama]

Hi Leslie,
Thanks a lot for your replies. I've sent you a private email as I
didn't really want to fill up this thread with my stupid questions and
to conform a couple of things that are probably obvious to other
here.

I've have also started a page here:
http://web.me.com/lord_philip/other_computers/System_80_4020.html
So that I can more easily share my findings.

So far I have only taken a reading from Z47 pin 13 which is described
in the manual as positive pulses derived from Raw_Data with 200nsec
width. You can see the reading from this pin on my page.

Thanks again.

Phil

[Nama]

> Data separator circuit in the X4020 is made of 3 one-shot's which
> use simple R/C networks to determine their timing/duration etc.
> It's possible that with age, the timing parameters have gone out
> of spec.
> Disabling the data separator may isolate that as a cause of it not
> working correctly.
>
> Temporarily disabling the data separator in the X4020 may help
> to get it working, at least temporarily.

I have located the J1, J3 and J4 jumpers, and I think that doing this
mod to temporarily disable the data separator circuit will be
relatively easy. I'm just curious as to what I should do or check for
after I have disabled this circuit?

Cheers
Phil

[Terry Stewart]

Interestingly one of my expansion units had the data separator disabled when i aquired it!  it didnt work until i reactivated it.  It took me days and days to discover the cause. I wrote a blog article about it.

Im not sure if this is the unit you have philip or if its revevant.  I just know the unit didnt work with the data separator disabled and suddenly worked when it did.  Anyway you might want to check the blog article as it talks about the circuitry. Sorry i can't cut and paste the link in.  Im typing this on a mobile phone and even that is chsllenging enough :-)

[Knut]

Hi

In the EI manual; Introduction for the EG3021 Double Density Adapter tells you
to remove J1-1 and J4 and connect J1-2. The DDkit does its own data separation
and won't work without the jumper change. I wonder if something about that also
came with the DDkit (should be somewhere...)

That EI was probably used with a DDkit.

BTW the Tandy EI did not have data separation and works ok. You got data
separation only with DDkits. EACA improved on Tandy design.

Knut

[Knut]

Hi again

Just a note on what I wrote in the BTW: The Tandy EI used the internal data
separation XTDS\ is pulled high by a 10K resistor with some other signals. DD
kits pull this signal low so external data separation can be used on the 1771 as
well as the 1791 which needs external data separation.

You can enable the internal data separation on the EACA EI too by removing J3
and disabling the external data separator... Now it enables you to test without
external data separator (with 1771 only).

I don't think the floppy controller will work without data separation for 1771
it must be either external or internal.

Knut

[Nama]

Thanks again for the replies.
Finally I had some time today to absorb what you have all been saying.
I didn't realize that the 4020 had both internal and external
separators available. Sorry for being so dumb...it happens from time
to time I'm afraid.

Tonight I removed J3 and J4 and switched J1 so that Pin 2 of Z58 feeds
into pin 27 of the 1771...Quite simple to do.

Unfortunately it didn't change anything, a DOS formatted disk still
does not load and the screen remains as before :-(

Phil

[Nama]

Not sure if this is significant, but I took some power readings from
where the voltages come into the board at the power connector.

The -16V line reads -21V
The +16V line reads 21V
and the +8V line reads 9V

[Nama]

...but I must add that the 5V line and 12V lines look pretty good, so
the regulators must be doing their job.

[Nama]

I removed the Canon/Sankyo drive and plugged in my Shugart SA400
drive. Basically unlike the Canon drive the Shugart does not spin
constantly. When Restet is pushed the drive spins up for 4 seconds and
then stops, so no change there. However this time I noted that the
drive light on the SA400 does not light up at all. I'll look into what
this means a bit more, but if anyone has any insight, or any ideas on
what next to test, I'm all ears.

Cheers again

Phil

[Terry Stewart]

Phililp do you have any other 5.25 inch drives? It would be good to
eliminate the IE or the drives as being good. At the moment it could
be either. It could be that the Canon drive has developed a fault and
the OSI one may be unusable anyway. I know that for the IE to work in
the absence of a double density mod, it has to have it's internal data
separator operating so (apart from any specific testing) I would re-
instate that.

Was that Canon a single sided drive, or a double sided one?

Terry

[Nama]

Hi Terry,
I haven't yet used the OSI MPI 51 drive with the System 80 setup yet.
I have tried the Canon drive and the Shugart drive. Unfortunately I
only have these three 5.25" drives.

Cheers

[Terry Stewart]

Are they both single sided or double sided?  Which is the one I prepared the disks on?  Was it the Canon?

Terry

[Nama]

The Canon drive was the one that you made the disks on. I don't know
if it is double sided or not, but at it is a newer half height drive
I'd imagine it's double sided. I have tried flipping the DOS boot disk
upside down incase that made any difference. It didn't. If you recall
it also has a switch on the back that we believed changed it from 40
track to 80 track. I've tried both positions.

The Shugart drive is single sided 40 track...a very basic drive.

[Terry Stewart]

If it it double sided (let's assume it is) then the Shugurt single sided drive won't boot off those NEWDOS disks.  The PDRIVE parameters will be expecting a double sided drive.  This will expain why the Shugurt won't work.  The odds of the drive being at fault or the interface are now 50:50.

The good thing though is that you should be able to replace it with a conventional PC 360k DD (not HD) drive.  These drives are 40 track, double sided and rotate at 300RPM.  This should be the same as the Canon drive (assuming it is double sided and the disks I made up were for a double sided drive).

Correct me if I'm wrong anyone, but I believe this is the case.

If you open up the Canon drive you should be able to see two heads.  As you say, all half height drives I've seen are double sided.

Terry

[Nama]

Thanks for the explanation Terry,
I guess I should start looking for another drive so that I can, at the
very least, rule it out it as part of the issue.
Most on eBay seem to be priced way high, especially when adding the
shipping to Japan also.
I've tried looking on some Japanese auction sites too, but the choice
seems limited, and the descriptions of the drive vague. Will keep
searching.

Cheers
Phil

[Leslie Ayling]

Hi Phil, et al.

Sounds like the SA400 is not being selected properly.

If the drive spins up for 4 seconds, it is getting the MOTOR_ON signal from
the interface OK.
If the drive light is not coming on, then it's not getting the DRIVE_SELECT
line.

Are you using a 34-way cable with *all* signals connected to all pins, or a
"position dependant" cable?
DSE cables had all signals connected on all drive connectors, and used the
jumper
on the drive to do the drive selection.

The Tandy drive cables had pins missing to do the selection. Tandy drives
had all
drive select jumpers installed, which meant the drive number depended on
which
connector it was plugged into.

More info here: http://tim-mann.org/trs80faq.html#[19]

Cheers,
Leslie

-----Original Message-----
From: eaca-di...@googlegroups.com
[mailto:eaca-di...@googlegroups.com] On Behalf Of Nama
Sent: Saturday, 4 February 2012 10:51 PM
To: Eaca discussion
Subject: Re: System 80 4020 expansion unit issues

Cheers again

Phil

--

[Nama]

Hi all,
The cables I am using are the ones that came with the unit from Terry,
and previously worked fine.
I checked the drive select 0 line again, and it seems to be doing all
the right things. High then goes low for 4 seconds and returns high.

I have just ordered a new 1771 incase this controller IC is the
problem, or at the very least I can eliminate it as a problem when
moving forward. I have asked on VCF if anyone has a spare 360k DD
drive also, and I have had a couple of replies, so if the new 1771
does not fix the issue then I may get one of these drives.

I really want to fix this expander unit as I really hate having
something in my collection that is not working. I'm sure you all
understand my feelings. I'll keep you informed of any progress.

Phil

[Terry Stewart]

Phil,

If the canon drive is a 40 track, double sided drive, you should be able to throw it into an standard PC and check if it reads and writes properly (as a 360k drive).  At least then you can eliminate the drive from the equation.  If it doesn't work in a PC, it's probably the drive that's at fault.

Terry

[Nama]

Unfortunately I don't have access to a desktop PC. I'm all Macintosh
here and the only PC i do have is a laptop that I use to connect to my
EPROM burners and such via it's Parallel connector. Maybe I could
borrow one from someone, or grab one that someone is throwing out. Now
my only concern would be space...I'm seriously running low on physical
space to actually put stuff. These Japanese apartments are rather
small.

:-(

[Nama]

The new 1771 arrived today. I promptly installed it. Unfortunately it
did not change anything :-(

[Nama]

Hi,
Me again.
I did some more poking around with my logic probe this evening.
Basically just looking for obvious weird signals.
I don't know how significant this is but Z40 (7416) has 4 lines coming
into it and seems to be an inverter who's output is DS1 thru DS4.
I get the following signals.

INPUT OUTPUT
1 (Low) 2 (High)
9 (Low) 8 (Nothing. No readable signal)
11(Low) 12 (Nothing. No readable signal)
13(Low) 14 (High)

(NB non of these pins seem to be pulsing)

Is there something suspect about the outputs on pin 8 and 12?
You can see this part of the schematic here:

http://web.me.com/lord_philip/other_computers/System_80_4020.html#3

Cheers
Phil

[Terry Stewart]

I don't know the significance either but, like you, I would consider it suspicious.

I was puzzled by the circuit diagram though Phil as it seems to show a mod on those lines?  That doesn't reflect what's actually on the physical expansion unit does it?

The standard circuit diagram is here.

Terry

Phil

[Nama]

Thanks for the schematic. I can actually read this version!!!! That
mod is not on my board, and was something that was hand drawn on the
diagram I was using.
Now that I can read the pin numbers better (and it's not late at
night), I just need to make a small amendment to my above post:

INPUT OUTPUT
1 (Low) 2 (High)
9 (Low) 8 (Nothing. No readable signal)

11(Low) 10 (Nothing. No readable signal)
13(Low) 12 (High)

I also removed the floppy from the loop by removing the cable incase
there was something about the floppy which was causing the Drive
Select outputs from Z40 (74LS16) to become funky, but that didn't
change anything as the outputs on pin 8 and 10 were still missing.
Anyway, I realize that these are the Drive Select lines, and the DS1
line seems to be working ok, however it is certainly strange. Maybe
I'll try piggybacking a 74LS16 over the existing one and see if that
does anything...

On Feb 19, 5:08 am, Terry Stewart <te...@webweavers.co.nz> wrote:
> I don't know the significance either but, like you, I would consider it
> suspicious.
>
> I was puzzled by the circuit diagram though Phil as it seems to show a mod
> on those lines?  That doesn't reflect what's actually on the physical
> expansion unit does it?
>
> The standard circuit diagram is

> here<http://www.classic-computers.org.nz/system-80/manuals_tm3_drawing%204...>
> .

[Terry Stewart]

I just measured those pins on Z40 on my own expansion box.  This was with no drives plugged in (and no computer plugged in).

I got

INPUT  OUTPUT

1=L      2=NOTHING
9=L      8=NOTHING
11=L   10=NOTHING
13=L   12=NOTHING

I don't understand how those select lines work but perhaps in order for these lines to show a signal, drives need to be plugged in, turned on and selected as drives 1,2,3 or 4.  Perhaps some jumper or setting in the drive activates these lines.  If this is the case, it's strange that you have a signal both on D4 and D1.  Did you have two drives connected (set on drive 1 and drive 4)?

Of course that might not be the correct interpretation but those are the signals I get.

Terry

[Nama]

Thanks for looking into that. I really appreciate it.
When I don't have the computer turned on, all (input and output) lines
are low except 8 and 10 which still show nothing.
When I unplug the computer completely from the expansion unit I get
the same results as you with all outputs not showing any signal.

Now when everything is plugged back in and I press reset, pin 1 goes
high, causing pin 2 to go low (which I guess is what you would
expect). No other lines are effected.

Maybe what I'm seeing is normal functionality on pins 8 and 10?

> Did you have two drives connected (set on drive
> 1 and drive 4)?

No, nothing like that, just the same setup as I've always had.

Phil

[Peter Nield]

The TTL 7416 is hex inverter buffer/driver with open collector - they are used to pull a bus line low, so the bus line needs a pull-up to maintain a logic 1 - which will be in the drive in this case.

From: Terry Stewart

Sent: Sunday, February 19, 2012 2:46 PM

To: eaca-di...@googlegroups.com

Subject: Re: System 80 4020 expansion unit issues

[Nama]

Aaaah...ok, thanks Peter,
I guess I was chasing the wrong ghost.

Cheers

Phil

[Peter Nield]

Hi Nama,

You may find getting your hands on a logic analyser/analyzer will help trace
things. Then you can see if the problem is what happens with the data,
though you may be able do that with the logic probe by tracing the data path
to make sure it is pulsing all the way to the read data line on the 1771, at
a guess.

I bought a Open Logic Snffer to help with tracing the video fault on one of
mine last year

--------------------------------------------------
From: "Nama" <forum...@mac.com>
Sent: Sunday, February 19, 2012 6:06 PM
To: "Eaca discussion" <eaca-di...@googlegroups.com>

Subject: Re: System 80 4020 expansion unit issues

> Aaaah...ok, thanks Peter,

[Terry Stewart]

I'm a bit confused now Phil.

As I understand things so far, you only have one drive attached (presumably configured as Drive 1).  Why then is pin 12 on D4 high as you indicated when you published the figures?  Shouldn't it be showing no signal.  It should only be high if (1) the logic gate was malfunctioning or (2) the drive pulling it high.  And the drive shouldn't be pulling it high on that D4 line, yes? 

Terry

On Sun, Feb 19, 2012 at 7:18 PM, Peter Nield <pj_n...@hotmail.com> wrote:

Hi Nama,

You may find getting your hands on a logic analyser/analyzer will help trace things.  Then you can see if the problem is what happens with the data, though you may be able do that with the logic probe by tracing the data path to make sure it is pulsing all the way to the read data line on the 1771, at a guess.

I bought a Open Logic Snffer to help with tracing the video fault on one of mine last year

--------------------------------------------------
From: "Nama" <forum...@mac.com>
Sent: Sunday, February 19, 2012 6:06 PM

To: "Eaca discussion" <eaca-discussion@googlegroups.com>

Subject: Re: System 80 4020 expansion unit issues

Aaaah...ok, thanks Peter,
I guess I was chasing the wrong ghost.

Cheers

Phil

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[Nama]

Thats a good point.
I think, and please correct me if I'm wrong, that the DS lines are
active low, therefore when I press reset, pin 1 goes high, causing pin
2 (DS1) to go low which makes drive 1 selected.
Pin 13 is low, and pin 12 is high, and these are unaffected by
pressing reset. So I guess this means DS4 is not selected.
Now why DS4 has a high signal, yet DS2 and DS3 have no signal is a
very good question indeed!!!

Phil

On Feb 19, 6:52 pm, Terry Stewart <te...@webweavers.co.nz> wrote:
> I'm a bit confused now Phil.
>
> As I understand things so far, you only have one drive attached (presumably
> configured as Drive 1).  Why then is pin 12 on D4 high as you indicated
> when you published the figures?  Shouldn't it be showing no signal.  It
> should only be high if (1) the logic gate was malfunctioning or (2) the
> drive pulling it high.  And the drive shouldn't be pulling it high on that
> D4 line, yes?
>
> Terry
>
>
>
>
>
>
>
> On Sun, Feb 19, 2012 at 7:18 PM, Peter Nield <pj_ni...@hotmail.com> wrote:
> > Hi Nama,
>
> > You may find getting your hands on a logic analyser/analyzer will help
> > trace things.  Then you can see if the problem is what happens with the
> > data, though you may be able do that with the logic probe by tracing the
> > data path to make sure it is pulsing all the way to the read data line on
> > the 1771, at a guess.
>
> > I bought a Open Logic Snffer to help with tracing the video fault on one
> > of mine last year
>

> > ------------------------------**--------------------
> > From: "Nama" <forums6...@mac.com>

> > Sent: Sunday, February 19, 2012 6:06 PM

> > To: "Eaca discussion" <eaca-discussion@googlegroups.**com<eaca-di...@googlegroups.com>

>
> > Subject: Re: System 80 4020 expansion unit issues
>
> >  Aaaah...ok, thanks Peter,
> >> I guess I was chasing the wrong ghost.
>
> >> Cheers
>
> >> Phil
>
> >> --
> >> You received this message because you are subscribed to the Google Groups
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> >> To post to this group, send email to eaca-discussion@googlegroups.**com<eaca-di...@googlegroups.com>
> >> .

> >> To unsubscribe from this group, send email to

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> >> .
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> >> group/eaca-discussion?hl=en<http://groups.google.com/group/eaca-discussion?hl=en>
> >> .

>
> > --
> > You received this message because you are subscribed to the Google Groups
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> > .

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> > For more options, visit this group athttp://groups.google.com/**
> > group/eaca-discussion?hl=en<http://groups.google.com/group/eaca-discussion?hl=en>
> > .

[Nama]

Peter,
Funny you should mention that, as Leslie sent me a private mail saying
exactly the same thing...So I've been looking into investing in a USB
logic analyzer...although I have no idea how to actually use one, or
decode it's output into anything meaningful!

I found a pretty cheap one in Akihabara for 8800yen called a Logic
Cube from Korean company called Zeroplus.

Phil

On Feb 19, 3:18 pm, "Peter Nield" <pj_ni...@hotmail.com> wrote:
> Hi Nama,
>
> You may find getting your hands on a logic analyser/analyzer will help trace
> things.  Then you can see if the problem is what happens with the data,
> though you may be able do that with the logic probe by tracing the data path
> to make sure it is pulsing all the way to the read data line on the 1771, at
> a guess.
>
>  I bought a Open Logic Snffer to help with tracing the video fault on one of
> mine last year
>
> --------------------------------------------------

> From: "Nama" <forums6...@mac.com>

[Peter Nield]

Open login sniffer is US$50.

--------------------------------------------------
From: "Nama" <forum...@mac.com>
Sent: Monday, February 20, 2012 1:05 AM

[Peter Nield]

Then again, the one you mentioned is probably a more commercial unit.

[Terry Stewart]

I'm thinking maybe circuitry in the drive is erronously setting that
DS4 line high, hence confusing the system? Are the jumpers in the
drive set correctly?

I don't have time in the next day or two but towards the end of the
week I could set up my own System 80 with an expander unit and a drive
and see what those readings on my machine are.

Terry

> To post to this group, send email to eaca-di...@googlegroups.com.

> To unsubscribe from this group, send email to

> eaca-discussi...@googlegroups.com.

> For more options, visit this group at

> http://groups.google.com/group/eaca-discussion?hl=en.
>
>

[lay...@bigpond.net.au]

Hi Phil, Terry, Peter, et al.

With the drive cable disconnected, you can still perform a simple test.

Using a 4.7K ohm resistor, tie pin2 of U40 (7416) to 5V somewhere on the board.
While resetting the system, use the logic probe to measure the signal on Pin2 of U40.
It should go low for a few seconds, then return high.

To test the other drive select lines:

If you reset into BASIC, you can perform the same tests using :
POKE 14304,x (Drive select latch at &H37E0)
where X is :

DS0 = Bit 0, x = 1
DS1 = Bit 1, x = 2
DS2 = Bit 2, x = 4
DS3 = Bit 3, x = 8

(DSE manuals call the signals DS1-DS4, but I find it easier using the Zero-based array numbers)

Poking ZERO will turn them all off again.

You will need the pull-up resistor on the appropriate output of U40 that you want to test since (as Peter mentioned) U40 (7416) is an open collector output.
Meaning: it doesn't actively drive any voltage but can pull a line low.

---

Phil, I noticed you mentioned that U40 pin 12 (DS3) was High without a drive connected?
That is unusual.
DS3 was commonly used as a side select signal when double sided drives became available.
The X-4020 lets you use any of the drive select lines as a side-select signal incidentally, depending on how Jumper J5 is set.

Does J5 have any jumpers installed?
Has someone soldered a wire from Pin32 of the drive connector to Pin6 (side select) by any chance?

Hope this helps.
Leslie

[Terry Stewart]

Leslie,

Pin 12 of U40 according the circuit diagram appears to go to DS4? See
http://www.classic-computers.org.nz/system-80/manuals_tm3_drawing%204.12_X4020%20expander%20schematics_sheet%203.jpg

You may have been thinking of the old TRS-80 convention of naming
drives from 0 to 3 (hence DS4 refers to Drive 3).

Cheers

Terry

[Nama]

Actually I mentioned that when no drive was connected the results were
the same as what Terry gets...which is to say, no signals on any of
the outputs. Once a drive is connected the output of pin 12 is high
but does not change on reset, and the output of pin 2 is high but goes
low for about 4 seconds on reset. The outputs on 8 and 10 still show
nothing.

I should have a 4.7K ohm resistor somewhere, so I'll try your other
suggestions sometime later today.

Cheers again



On Feb 20, 7:15 am, "layl...@bigpond.net.au" <layl...@bigpond.net.au>
wrote:

> ---- Peter Nield <pj_ni...@hotmail.com> wrote:
>
>
>
>
>
>
>
> > The TTL 7416 is hex inverter buffer/driver with open collector - they are used to pull a bus line low, so the bus line needs a pull-up to maintain a logic 1 - which will be in the drive in this case.
>
> > From: Terry Stewart
> > Sent: Sunday, February 19, 2012 2:46 PM
> > To: eaca-di...@googlegroups.com
> > Subject: Re: System 80 4020 expansion unit issues
>
> > I just measured those pins on Z40 on my own expansion box.  This was with no drives plugged in (and no computer plugged in).
>
> > I got
>
> > INPUT  OUTPUT
>
> > 1=L      2=NOTHING
> > 9=L      8=NOTHING
> > 11=L   10=NOTHING
> > 13=L   12=NOTHING
>
> > I don't understand how those select lines work but perhaps in order for these lines to show a signal, drives need to be plugged in, turned on and selected as drives 1,2,3 or 4.  Perhaps some jumper or setting in the drive activates these lines.  If this is the case, it's strange that you have a signal both on D4 and D1.  Did you have two drives connected (set on drive 1 and drive 4)?
>
> > Of course that might not be the correct interpretation but those are the signals I get.
>
> > Terry
>

[Knut]

Hello

I guess you mean what is Z41 in my schematics...

This is an open collector output and the terminator is the pullup. All outputs
to the drives are open collector and are being pulled up by the terminator.

The open collector and pullup is used because the lines are expected to be long.

To see the actual signal you need to attach a drive with terminator...

As you see, a terminator is necessary for the floppydrives to work correctly.
When we used NMOS inputs 74xx or 74LSxx the inputs pull high very weakly so a
drive might work but would also be very susceptible to noise.

Note that PC floppy system is different so every drive is terminated with a
higher ohm terminator - nasty, but works for short cables.

Knut

[Nama]

Hi Leslie,
I was able to find a 4.7k resistor and try out your trick.
Basically every line, pins 2,8,10 and 12, all dropped low for about 4
seconds upon poking the correct addresses. So I guess there is nothing
wrong with Z40 after all.
Very handy tip by the way.

As for the drive jumper settings, they are as follows:

SH
AH - Jumper here
S1 - Jumper here
S2
S3
S4

Not sure what SH and AH actually stand for though.

Maybe time to get myself a cheap logic analyzer.

On Feb 20, 7:15 am, "layl...@bigpond.net.au" <layl...@bigpond.net.au>
wrote:

> ---- Peter Nield <pj_ni...@hotmail.com> wrote:
>
>
>
>
>
>
>
> > The TTL 7416 is hex inverter buffer/driver with open collector - they are used to pull a bus line low, so the bus line needs a pull-up to maintain a logic 1 - which will be in the drive in this case.
>
> > From: Terry Stewart
> > Sent: Sunday, February 19, 2012 2:46 PM
> > To: eaca-di...@googlegroups.com
> > Subject: Re: System 80 4020 expansion unit issues
>
> > I just measured those pins on Z40 on my own expansion box.  This was with no drives plugged in (and no computer plugged in).
>
> > I got
>
> > INPUT  OUTPUT
>
> > 1=L      2=NOTHING
> > 9=L      8=NOTHING
> > 11=L   10=NOTHING
> > 13=L   12=NOTHING
>
> > I don't understand how those select lines work but perhaps in order for these lines to show a signal, drives need to be plugged in, turned on and selected as drives 1,2,3 or 4.  Perhaps some jumper or setting in the drive activates these lines.  If this is the case, it's strange that you have a signal both on D4 and D1.  Did you have two drives connected (set on drive 1 and drive 4)?
>
> > Of course that might not be the correct interpretation but those are the signals I get.
>
> > Terry
>

[Leslie Ayling]

Hi Phil,

You've managed to eliminate most things that you could possibly test with a
probe.
Logic analyzer is going to come in handy I think.

Still would like to see if those drives work in a another PC or not.
Haven't really established conclusively whether the drives are functional...

Cheers,
Leslie

-----Original Message-----
From: eaca-di...@googlegroups.com
[mailto:eaca-di...@googlegroups.com] On Behalf Of Nama

[Nama]

Bit the bullet and got myself a logic analyzer...now how to figure out
how to use it!!!

Phil