SA801 bringing down to Shugart 34 pin interface issue

Tuc · Jul 24, 2024

Hello,

Trying to connect an SA801 to a standard 34 pin Shugart bus. (TRS-80 Model I). I’ve tried and it's just not working so hopefully someone can point out where I’ve gone wrong.

The SA801 was just checked, lubed, tested by a local company. I put it in a case with a new PS and connectors after it came back.

The jumpers on the SA801 when I got it back -

Y/Z	Y
800/801	800
DS/HL	DS
T1	Jumpered
A	Jumpered
B	Jumpered
X	Jumpered
DC/Pin 12	Open
D/Pin 16	Open
C/Pin 18	Open
I/Pin 20	No jumper, pads
R/Pin 22	Open
S/Pin 24	Pad
DS1/26	Jumpered
T2 (After DS1)	Jumpered
DS2/28	Open
DS3/30	Open
DS4/32	Open
T3/34	Jumpered
T4/36	Jumpered
T5/38	Jumpered
T6/40	Jumpered
RR	Jumpered

I closed all jumpers marked “Open” since I figured it was easier to control it externally than internally.

I bought 2 IDC’s, a 34 pin and a 50 pin. I connected all the 34 side grounds (1-33) to the same pin on the 50 side. I then jumpered 33 to 35, 35 to 37, etc until I got to 49, and I jumpered that to 1.

I then connected

34 pin	34 Signal Name	50 pin
2	/DCD	2 or GND depends, tried both
4	INUSE	X
6	/DS3	X
8	/INDEX	20
10	/DS0	26
12	/DS1	28
14	/DS2	30
16	/MTRON	GND or (16 or 18) - Problem
18	/DIR	34
20	/STEP	36
22	/WDATA	38
24	/WGATE	40
26	/TRK00	42
28	/WPT	44
30	/RDATA	46
32	/SIDE1	32
34	/RDY	22

32 is straight through since the TRS-80 needs Drive Select 3 to be on 32. (As opposed to 6)

My first issue is that if I plug this into an off computer, with drives at 0 and 2, with 34/2 to 50/2 for DCD, and 34/16 to 50/GND, 50/16 or 50/18 it starts spinning the motor on drive 2 (I can’t tell 0, it’s a virtual drive)

So 2nd problem is that if I just leave it with 34/16 unconnected, and try to boot the computer, it fails. If I remove the 50 pin connector, it fails to boot. If I remove the 34 pin connector, I can boot again.After it boots if I put the 34 pin connector back in, it still works. If I put the 50 back, it stops.

Any starts for debugging?

Thanks, Tuc

VeryVon · Jul 24, 2024

On a Model 2, Drive 0/A I would map:

Motor Enable A (pin 10) -> Head Load (pin 18)
Drive Select A (pin 14) -> DS0 (pin 26)

p.s. not sure if this works on a Model 1 controller

EDIT: Disregard this message, for some reason i'm quoting PC->8" Shugart pin mappings, ooops!

ldkraemer · Jul 24, 2024

The Model 1 has the Drive Select Pins PULLED from the cable except for the Specific Floppy Drive
at specific places on the Floppy Cable.

Code:

TRS-80 Model 1 Floppy Disk Controller Signals to Radio Shack Drives 


Pin No. Signal Name Description
1 Ground --
2 N/C Connector Clamp (Not used on TRS-80 Model 1 Floppy Disk Controller FDC)
3 Ground --
4 N/C Reserved (Not used on TRS-80 Model 1 Floppy Disk Controller FDC)
5 Ground --
6 N/C Reserved (Not used on TRS-80 Model 1 Floppy Disk Controller FDC)
7 Ground --
8<-- /IndexNINDEX/SECTOR (0=Index)
9 Ground --
10--> /NDS1 0=Drive Select 0 (Physical Drive 1 = External)
11 Ground --
12--> /NDS2 0=Drive Select 1 (Physical Drive 2 = External)
13 Ground --
14--> /NDS30=Drive Select 2 (Physical Drive 3 = External)
15 Ground --
16--> /MOTEB 0=Motor Enable Drive 1
17 Ground --
18--> /DIR 0=Direction Select
19 Ground --
20--> /Step 0=Head Step
21 Ground --
22--> /WDATA Write Data
23 Ground --
24--> /WGATE Floppy Write Enable, 0=Write Gate
25 Ground --
26<-- /TRK00 0=Track 00
27 Ground --
28<-- /WPT 0=Write Protect
29 Ground --
30<-- /RDATA Read Data
31 Ground --
32--> /NDS4 0=Drive Select3 (Physical Drive 4 = External)
33 Ground --
34 N/C Connector Clamp (Not used on TRS-80 Model 1)

Pins 2, 4, 6, 34 SPARE in J5 Floppy Disk Bus

Larry

ldkraemer · Jul 24, 2024

This should be close if you only connect the DRIVE SELECT that you need. Leave the others
NOT CONNECTED.

Code:

TRS-80 Model 1 Floppy Disk Controller Signals to Radio Shack Drives

Pin No.         Signal Name     Description            SA801
2                N/C            Connector Clamp N/U
4                N/C            Reserved   N/U
6                N/C            Reserved   N/U
8<--           /Index          NINDEX/SECTOR            20 INDEX
10-->         /NDS1         0=Drive Select 0             26 DS0 As Needed
12-->         /NDS2         0=Drive Select 1             28 DS1 As Needed
14-->         /NDS3         0=Drive Select 2             30 DS2 As Needed
16-->         /MOTEB      0=Motor Enable Drive 1         18 Head Load
18-->         /DIR            0=Direction Select          4 Direction
20-->         /Step           0=Head Step                36 Step
22-->         /WDATA      Write Data                     38 Write Data
24-->         /WGATE     Floppy Write Enable             40 Write Enable
26<--         /TRK00      0=Track 00                     42 TRACK 0
28<--         /WPT         0=Write Protect               44 Write Protect
30<--         /RDATA      Read Data                      46 Read Data
32-->         /NDS4       0=Drive Select 3               32 DS3 As Needed
34             N/C           Connector Clamp N/U
                                                         12 No Connect
                                                         16 No Connect
                                                         22 No Connect
                                                         24 No Connect
                                                         48 No Connect
                                                         50 No Connect
Pins 2, 4, 6, 34 SPARE in J5 Floppy Disk Bus

Larry

ldkraemer · Jul 25, 2024

Terminators T3, T4, T5, & T6 need to be used for the last drive in the system.

There are also specific jumpers on the Drive Logic board that need to be used for Drive select.
Ref: the Schematic for the SA-801

39025-1_SA800_801_Service_Manual_Mar82.pdf - Shared with pCloud

Keep, share and access your files whenever you need from wherever you are. Create a free pCloud account and make your life easier.

u.pcloud.link

Larry

Tuc · Jul 29, 2024

VeryVon said:
On a Model 2, Drive 0/A I would map:

Motor Enable A (pin 10) -> Head Load (pin 18)

Drive Select A (pin 14) -> DS0 (pin 26)

p.s. not sure if this works on a Model 1 controller

EDIT: Disregard this message, for some reason i'm quoting PC->8" Shugart pin mappings, ooops!

Thats been the biggest issue. I bought like 5 34<>50 converters, and they'all all PC. So used that as a base for the most part, and then got rid of the twist part.

Tuc · Jul 29, 2024

ldkraemer said:

This should be close if you only connect the DRIVE SELECT that you need. Leave the others
NOT CONNECTED.

Code:

TRS-80 Model 1 Floppy Disk Controller Signals to Radio Shack Drives

Pin No.         Signal Name     Description            SA801
2                N/C            Connector Clamp N/U
4                N/C            Reserved   N/U
6                N/C            Reserved   N/U
8<--           /Index          NINDEX/SECTOR            20 INDEX
10-->         /NDS1         0=Drive Select 0             26 DS0 As Needed
12-->         /NDS2         0=Drive Select 1             28 DS1 As Needed
14-->         /NDS3         0=Drive Select 2             30 DS2 As Needed
16-->         /MOTEB      0=Motor Enable Drive 1         18 Head Load
18-->         /DIR            0=Direction Select          4 Direction
20-->         /Step           0=Head Step                36 Step
22-->         /WDATA      Write Data                     38 Write Data
24-->         /WGATE     Floppy Write Enable             40 Write Enable
26<--         /TRK00      0=Track 00                     42 TRACK 0
28<--         /WPT         0=Write Protect               44 Write Protect
30<--         /RDATA      Read Data                      46 Read Data
32-->         /NDS4       0=Drive Select 3               32 DS3 As Needed
34             N/C           Connector Clamp N/U
                                                         12 No Connect
                                                         16 No Connect
                                                         22 No Connect
                                                         24 No Connect
                                                         48 No Connect
                                                         50 No Connect
Pins 2, 4, 6, 34 SPARE in J5 Floppy Disk Bus

Larry

Hi,

Ok, so as for T3/T4/T5/T6 , they're jumpered in the drive, and I am trying to use this on physical 4/logical 3 on this drive line.

I adjusted as you suggest. I only used 32/DS3 since thats where I want. It's jumpered for all 4 on the drive, but its my understanding between the pulled pin cable I have, the fact I'm not connecting the other 3 via the 34<>50 then I'm safe.

So I boot my system and attached the IDC34 side. things still work which is a good sign. But then I put the 50 side even with the unit off, and the drive thats physical 3/logical 2 starts its motor spinning and the system stops responding. If I turn the disk drive on and try, system won't boot anymore until I at least remove the 50 pin cable.

Any debugging I can do? I'm limited on equipment, but will do what I can.

Thanks!
Tuc

Tuc · Jul 29, 2024

@ldkraemer - Some more reasoning for my original pinning.

Pin 2 - One of the 34<>50 devices I bought claims Shugart/34 pin 2 is "/CDC /REDWC". Shugart/50 pin 2 is "/TG43 /REDWC". The device has a jumper that if you need either disk density (/REDWC) or TG43 to connect it. , otherwise it can be left open or grounded. I believe the 801 doesn't need TG43, and I'm running everything at low density ANYWAY, so I guess that really wasn't needed.

Pin 16 - This was very confusing, yea. Shutgart/34 says its /MTRON . The device that was doing this for the PC had a jumper for HLD (Head Load) that if selected went to Shugart/50 pin 18 HLD. But it'd also was connected to DLOCK (Disk Lock) that if jumpered went to Shugart/50 pin 16 DLOCK.

Pin 18 - My pictures are showing Shugart/34 pin 18 and Shugart/50 pin 34 are both "/DIR". My documentation says Shutgart/50 pin 4 is NC, so I'm a bit confused by this change.

Pin 34 - My diagram shows Shutgart/34 pin 34 is "/RDY /DC". The diagram for the PC shows if you want DC, send it to pin 12 of Shugart/50. If you want READY, its pin 12 of Shugart/50. I'm a bit confused about it being unconnected.

Thanks, Tuc

ldkraemer · Jul 30, 2024

Pin 2 - One of the 34<>50 devices I bought claims Shugart/34 pin 2 is "/CDC /REDWC". Shugart/50 pin 2 is "/TG43 /REDWC". The device has a jumper that if you need either disk density (/REDWC) or TG43 to connect it. , otherwise it can be left open or grounded. I believe the 801 doesn't need TG43, and I'm running everything at low density ANYWAY, so I guess that really wasn't needed.

You must remember that the Model 1 does not support the /REDWC, and that if you are doing READ ONLY you don't need this signal.
I would just connect the First Floppy as the BOOT DEVICE, and when it's booting properly then add the 8" Floppy Drive as DS1
in a DS{0..3} configuration. (If the second Floppy is marked as DS{1..4} then you select it as DS2.)

Boot from the First Drive and see if you can access the Second Drive.

What OS are you Booting? TRSDOS, NEWDOS, MULTIDOS, DOSPLUS, LDOS, DOUBLE DOS, or ?????
If you are booting NEWDOS, you have to configure the OS's PDRIVE command for the proper attached Floppy Drive.
And you have to make the PDRIVE's setting active by using the A switch.

PDRIVE :0
change as needed then
PDRIVE :0,A
(I'm going strictly from memory 40 years ago, so I might have some errors in the above command's.)
The NEWDOS Manual spells out exactly what's needed.

I'm not familiar with the other OS's, so you will need a Manual to guide you through those steps.

Pin 34 - My diagram shows Shutgart/34 pin 34 is "/RDY /DC". The diagram for the PC shows if you want DC, send it to pin 12 of Shugart/50. If you want READY, its pin 12 of Shugart/50. I'm a bit confused about it being unconnected.

The Model 1 doesn't support RDY - DC.

Does your Model 1 have the Double Density Controller?

I am thinking there was a limit of three floppy drives on the Model 1, but don't remember the reason.

Larry

Tuc · Jul 30, 2024

ldkraemer said:
You must remember that the Model 1 does not support the /REDWC, and that if you are doing READ ONLY you don't need this signal.

No worries, just explaining why I had it there in the first place.

ldkraemer said:
I would just connect the First Floppy as the BOOT DEVICE, and when it's booting properly then add the 8" Floppy Drive as DS1
in a DS{0..3} configuration. (If the second Floppy is marked as DS{1..4} then you select it as DS2.)

Boot from the First Drive and see if you can access the Second Drive.

Ok, will do. Something that I didn't mention that might be at play, is that the Physical 1/Logical 0 is a Gotek with Shugart Emulation running HXC2001 software (Not the more common FlashFloppy). There is no semblance of terminators on it that I'm aware of, but some places I look do mention there are ones. I have put a 2nd and 3rd drive (3rd drive is an SA-400, was terminated) and everyone was happy so didn't know if that was a fluke or by design.

I will move the SA-400 to Logical 0 and change its DS (Even with the pulled cable, just to be sure) and move the SA-801 to Logical 1 and change its DS also.

ldkraemer said:
What OS are you Booting? TRSDOS, NEWDOS, MULTIDOS, DOSPLUS, LDOS, DOUBLE DOS, or ?????

Right now it's a pristine copy of NewDos/80 V2.5 . Absolutely no zaps or tweaks. I have access to many of the other ones, so if there is a better one to debug/work with to prove it works, I'm willing to try!

ldkraemer said:
If you are booting NEWDOS, you have to configure the OS's PDRIVE command for the proper attached Floppy Drive.
And you have to make the PDRIVE's setting active by using the A switch.

PDRIVE :0
change as needed then
PDRIVE :0,A
(I'm going strictly from memory 40 years ago, so I might have some errors in the above command's.)
The NEWDOS Manual spells out exactly what's needed.

I'm not familiar with the other OS's, so you will need a Manual to guide you through those steps.

Yes, aware of that, but right now I can't get to the point of booting the OS with the SA-801 online. It seems to want to, I see the Gotek say "RA" (Random Access) but then nothing happens. When I do get the ability to boot an OS with the SA-801, I plan to do -

PDRIVE,dn1,dn2,TI=BH,TD=B,TC=77,SPT=17,TSR=3,GPL=3,DDSL=17,DDGA=6,A

Until then, I just want to get to a place where plugging the drive in doesn't cause it to not boot or freeze the system.

ldkraemer said:
The Model 1 doesn't support RDY - DC.

Does your Model 1 have the Double Density Controller?

Yes, I have an Aerocomp in there, but I haven't activated it for anything. I could pull it if it might be interfering.

ldkraemer said:
I am thinking there was a limit of three floppy drives on the Model 1, but don't remember the reason.

Larry

So there was "sort of" a limit. If you wanted to be able to use double sided drives, it needed pin 32 for that. If you wanted 4 drives, you needed a way to get pin 6 onto pin 32 since RS decided to use that as its DS3 instead of 6.

I'll follow up when I've re-cajiggered everything.

Tnx, Tuc

Tuc · Aug 1, 2024

Tuc said:
I'll follow up when I've re-cajiggered everything.

Tnx, Tuc

@ldkraemer - No go. No matter what, I didn't get any sort of light on the SA801, and having the converter plugged in produced inconsistent booting.

Is there any sort of devices I can put in between the cable(s) and the drive to see what signals are happening? I have a mini-logic analyzer, never used it. Is there anything I can attach to the SA801 to force signals?

Thanks, Tuc

ldkraemer · Aug 1, 2024

Yes, I figured it wouldn't work because all the the Jumper options there are on that drive.
Your wiring should be correct and Jumpers T3, T4, T5, and T6 INSTALLED are correct.
You also need Jumpers INSTALLED on C, and X (make sure Jumper Y & Z are REMOVED).
Now, REMOVE Jumpers DS1, DS2, DS3, and DS4 on the 8" drive. You also need Jumper T1
INSTALLED for Drive Select PULLUP Resistor.

Now, if the Floppy is inserted after Power UP, and the Door is then closed, when you do a DIR
of Drive :1 the LED should come on and the Head Load, and the Motor spin. I think the Spindle
motor always spins on an 8" drive, but I've never used or seen one.

I've attached the pages and Schematics you need to print and make up in yellow for installed
and red for removed Jumpers.

Give that a try. At least the LED should come on. You can troubleshoot the Signals with your
DC volt meter. The Signals are ACTIVE LOW, and the INPUT Signals to the Drive should have
PULLUP RESISTORS that Pull UP the Signals to +5 VDC if they are not ACTIVE.

Larry

ldkraemer · Aug 1, 2024

I closed all jumpers marked “Open” since I figured it was easier to control it externally than internally.

I wouldn't close all the jumpers thinking that will work, because this drive has a multitude of jumper
options. You MUST use the Schematic(s) to enable exactly what you want to get the drive to
react to what you want.

Larry

ldkraemer · Aug 2, 2024

A couple of other things come to mind when using the TRS-80 Model 1.

1. NEVER Power UP or DOWN with a Floppy In the Drive with the Door Closed on the Floppy(s).
2. ALWAYS use a Power Strip to Power the Brick(s) for the Model 1 so they are not sitting with
Power ON for days on end. That will shorten their life.

Also the Model 1 uses Drive Labels of DS{0..3} such that the Boot Drive is ZERO and your 5.25" or
8" can be used Drive 1. If using a Tandon TM-100 those Floppy Drives are labeled as DS{0..3}, which
makes sense. It also matches the TRS-80's label of :1, so you get a Directory with DIR :1.

But, if the 8" is used as Drive 1 it uses Drive Labels of DS{1..4} which must be strapped for the second
physical drive which is Drive 2 in a DS{1..4} configuration. So, DS1 for the Model 1 selects DS2 which
is the 8" floppy. (This still matches my Wiring in a previous post even though I labeled then as a typical
DS{0..3} versus the correct 8" labeling as DS{1..4}.

I hope this doesn't confuse you, as far as your wiring goes. I just stumbled across the slight error in the
drive labeling.

Larry

ldkraemer · Aug 2, 2024

In looking over the Schematic again, I found a mistake I made in a previous posting.

REMOVE Jumpers DS1, DS2, DS3, and DS4 on the 8" drive.

Should be REMOVE Jumpers DS1, DS3, and DS4 on the 8" drive.
Jumper DS2 has to be installed for the 8" Floppy Drive to be selected for the Model 1's
Drive :1.

Larry

Tuc · Aug 8, 2024

Haven't forgotten/ignored. My Model I isn't sending video sync signals anymore and given I'm not an electronics person, trying to find someone to help (Or just pay, I'm MUCH better at just paying.

)

Tuc · Oct 15, 2024

@ldkraemer et al.

Many apologies for the delay. Not that it matters, but the Model I was using developed video issues. I sent it away for repair, then I went on a cruise, then I got COVID on the cruise, then life got in the way, then Tandy Assembly, and then finally life. :-/ But everything is FAIRLY calm, so now I'm running back to this.

I decided given @ldkraemer's suggestions to do a reset. The drive was originally shipped as -

AD_4nXfP30iTwY1gYAe_DgcBfSOAGC8FEUOxJOJ4ncnNAtoQ2FPGZG9n1xcpuVWIyzT1LN8jWEX1RxdcqlS0ikUfX6F4VVla7LO6ZLO0WL8njEROVpJfdyQUnVzIG2SyUBr93h7YRplj6Ffx3G3wIwdPv7F0fdDL

There were a few options I saw that I might want to change, and given the hassle I have to go through to change the settings (They're on the side that mounts to the case/bottom. So every time I need to make a change I have to take everything apart) I decided to create -

Basically its 10 switches and I put Dupont female cables (Same color on each side of each switch)

I was going to connect it as -

Designator	Reason	Shipped	Switch num	Switch color	Position
T3,T4,T5,T6	Terminations for Multiplexed Inputs	All plugged			All Plugged
T1	Terminator for Drive Select	Plugged			Plugged
T2	Spare Terminator for Radial Head Load	Open	5	Green	OFF
DS1, DS2, DS3, DS4	Drive Select Input Pins	Plugged, Open, Open, Open	1,2,3,4	Blue, Purple, White, Yellow	AS NEEDED
RR	Radial Ready	Plugged			Plugged
RI	Radial Index and Sector	Plugged			Plugged (Solder trace)
R,I,S	Ready, Index, Sector Alternate Output Pads	Plugged			Plugged (I + S traces_
HL	Stepper Power From Head Load	Plugged	6	Grey	ON (DS is common, skipping and putting jumper on)
DS	Stepper Power From Drive Select	Open	7	Brown	OFF(HL is common, skipping)
WP	Inhibit Write When Write Protected	Plugged			Plugged (trace)
NP	Allow Write When Write Protected	Open			Open (open trace)
8,16,32	8, 16, 32 Sectors (SA801 Only)	8&16 Open, 32 plugged			8&16 Open, 32 plugged (Traces)
D	Alternate Input-In Use	Open	8		OFF
2,4,6,8,10,12,14,16,18	Alternate Input-In Use	Open			All Open (Cant find)
D1,D2,D4,DDS	Customer Installable Decode Drive Select Option	Open			All Open (Traces)
A,B,X	Radial Head Load	All plugged	9	Blue 2	A+B plugged, X ON (ldk wants on)
C	Alternate Input Head Load	Open	10	Purple 2	OFF (ldk wants ON)
Z	In Use from Drive Select	Plugged	New 6	Grey	ON (ldk wants OFF)
Y	In Use from HD LD	Open			Open (Either Z or Y, common gnd)
DC	Alternate Output-Disk Change	Open			Open
NFO	Non Force Out	Open			Open
TS	True FM Data Separation	Open			Open
800	Operate as SA800	Open			Plugged
801	Operate as SA801	Plugged			Open (Either 800 or 801, common gnd)

the reason I put some of the leads on the switch is because I saw things in the manual that made me think that once I got it working, I might want to try. So I originally set it up as mentioned, but in the middle realized that DS/HL shared a common, and didn't want to futz with that, so left them off.

I then went back and re-read @ldkraemer's messages. FYI, the attached files (Much appreciated, were not included with the copy of the manual I downloaded, so I had to search for the positions myself) didn't have anything red/yellow, so following only the text. "X" was request to be on, and I already planned to have it on. "C" (Alternate Input Head Load) is shipped open, but was requested to be put ON. So I moved that to the switch. Just the opposite for "Z". I also turned on ONLY switch 3 as I want it to be drive :2 (I totally understand the disparity in numbering, not the first time I've run into this with devices.

).

I then went back and re-read the pinning diagram. I do want to mention that I pinned the odd numbers from 1-33 on the 34 pin side to the corresponding number on the 50 pin side. I then connected the 50 pin #35 to 50 pin #37, 50 pin #37 to 50 pin #39, etc until I got to 50 pin #50, and then looped that back to 50 pin #1. While not exactly how drives do it (They'd all be looped together on each side) this should suffice (I hope). I did add all the DS lines from 34 to 50 like a non-pulled pin cable would have, but I'm only using one "DS", which should be acceptable.

So this is where I am, I think I now have exactly what's expected and mentioned to move forward. While I do plan to follow the rest of the instructions tomorrow, I also plan to build something I saw in - https://arduino.stackexchange.com/questions/3702/controlling-floppy-disk-drive-with-arduino . I ran out of Dupont wires which will be here tomorrow. I previously bought a 34 pin breadboard mounted header that I can use to make things cleaner.

I'll get back to it tomorrow, but I wanted to update everyone and thank anyone that's been watching/contributing for hanging in there.

Thanks, Tuc

Tuc · Oct 17, 2024

Order hasn't shown up yet ( :-/ ), but Uno is programmed, As soon as it does I'll go into the lab and try it first on my Gotek.

Eudimorphodon · Oct 17, 2024

Tuc said:
Yes, I have an Aerocomp in there, but I haven't activated it for anything. I could pull it if it might be interfering.

Going back a way in the thread to this, but... it's my at least vague understanding that the "bare" floppy controller in the Model I can't handle an 8" drive? 8" drives (even in single density) run at twice the data rate of contemporary 5.25" drives? IE, in order to read/write an 8" drive with the 1771 disk controller that's in the EI's standard single-density controller you have to feed a different clock into the disk controller. These limitation mean that in order to run an 8" floppy drive on a Model I you need to add an expansion board which adds this dual-clock capability (and, preferably, a better data separator than the one built into the 1771) to the machine. Here's some references:

FD1771 Datasheet. (Page 3, mentions that the clock should be 2mhz for an 8" floppy drive, 1mhz for a mini floppy)

LNDoubler 5/8 user manual: Theory of operations, page 26.

The OG add-8"-drive modification for the Model I was the Omikron Mapper II; I linked the LNDoubler first because its manual has the theory of operations page.

The Aerocomp doubler has a reputation in the old literature of being a good double density board, but I think it's pretty much a straight copy of the Percom DD board (they sold it as having a better data separator) and I don't recall it ever claiming to support 8" drives? The "normal" DD boards do have a higher clock present for double-density operation but I'm not sure they can use it for single density FM operation? I can't say I ever tried.

Tuc · Oct 17, 2024

@ldkraemer , @Eudimorphodon and others watching this,

Update... So it turns out that Arduino project probably never worked, so so much for that. I was hoping to have a test rig that would help take a lot of room for error out of the equation. Looks like it only added to it. :-/

So I took the fully pinned (TRS-80 cables have pulled pins to make DS easier, so it should never have seen the "unused" DS lines. I'm setting this as :3 on the machine, or depending on devices starting at 0 as DS2 and those starting at 1 as DS3. Plugged it in, and my machine wouldn't boot. Removed it, it would. I then tried -

Only 34pin edge to 34 pin - Fine
Added 34pin to 34 pin - Fine
34 pin to 34 pin connected to 50 pin - Fine
50 pin to 50 pin extension - Fine
50 pin extension to drive unit - Won't boot (I don't have 50pin male to 50 pin card edge, or 50 pin female to card edge, but will source.

SIGH. Ok, so to explain my testing, its basically booting from DS0 an operating system, and as I add more pieces doing a "DIR" to see if it works. Oddly, failure has my Gotek (Yes, I'm back to the Gotek, it also serves as a debug device). start going track by track up. I think I've mostly stopped it when it was seeking in track 150 of a 35 track disk!

So I then removed the extra DS lines. Gotek seeks track by track and I stop it at 150 (Actually have to turn the drive off for it to gain its wits again).

So I decided to pull all the even numbered wires, testing if there some weirdness with my grounding. Just having my grounding to each other, its fine. So I decided to go pin by pin from the 34 pin side. Everything is fine until I get to pin 16. Once I connect 16, it starts to exhibit the weird behaviour of constantly incrementing tracks. So I leave that disconnected. I continue until I've done all the 34 pin side of things except for pin 16. I put pin 16 back, and the problems start again. So there is something about head load its not happy about.

Just for sh!ts and giggles, I changed C and Z back to the defaults, and reconnected 16. It doesn't act funny! (Not exactly sure what that means yet). I immediately went to add the pdrive to see if I can get it act/react, but apparently my PDRIVE line is wrong. I get "**** TI= SPEC BETWEEN DRIVES INCOMPATIBLE . So I need to do more investigation. But...

@ldkraemer / et al - Any thoughts about all this?
@Eudimorphodon - I didn't forget you, but I'm late for a doctor appt. But I'm aware, I'll let you know how I'm addressing that .

Thanks!
Tuc

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SA801 bringing down to Shugart 34 pin interface issue

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