H17 Floppy Drive RAW Read/Write Z80 Controller!

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norberto.collado koyado.com

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Jul 9, 2021, 4:09:42 PMJul 9
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I started years ago on the idea to modify a bad H17 floppy drive to be controlled by a Z80 controller. The Z80 controller will communicate with the H17 controller, to read/write data to on-board RAM with battery backup. Also, it will control the floppy drive spindle, track zero detector, diskette media detector, and to be able to seek between tracks. 

I have several 5.25" bad floppy drives that I can use. The idea is to have the same feel and look like the original floppy drive. You just insert a floppy diskette and then the Z80 will emulate all floppy conditions. It is more like having the SVD-III controlling a real floppy drive.

The idea for using the Z80 is to use all the H17 code without the need to re-write that much. The goal is for my personal learning on floppy technology especially for the H17 controller as is the easy one to tackle. Also, to keep my H17 enclosure as original.

My question is: How easy is to interface to the floppy cables that controls the motors? I'm looking for a simple circuit design that can spin the floppy media (ignore RPM's), head load, and control the seek operation. The sensors should be easy to do (track Zero and floppy media presence) + drive LED.

This is the floppy drive that I have, and this will be next year project depending on how easy is to interface. I just want to take out the top board and insert the Z80 controller board and plug in the cables.


Douglas Miller

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Jul 9, 2021, 5:21:40 PMJul 9
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Interesting project. So, the floppy drive is just decoration? The "media" is some storage device (SD, CF, ...) attached to the Z80? There would be no diskette in the drive - or at least no diskette that contains data? I know the MAME simulators have gone overboard (or not?) with simulating audio, and have a lot of audio clips for floppy drives - maybe just add a speaker (and audio circuitry) and leave the drive dead (except for LED)?


As I recall, the motor might be a bit tricky. But if you only need to approximate RPM then maybe it can be simplified. Just a matter of some analog circuitry. Does head load exist on 5" drives? The ones I remember were always loaded - it was the 8" drives that actually loaded/unloaded the heads. LED should be pretty basic, I presume.


I suppose it doesn't need to actually be a Z80 in the controller, either? Could be an rPi running Linux?

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Glenn Roberts

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Jul 9, 2021, 5:35:59 PMJul 9
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The early 100k 5-1/4” drives had head load solenoids. I always cringed a bit hearing them load and unload when assembling some code.

But if you put a z80 cpu in the shell of one of those old drives and had it cycle the head load for effect it would sure be reminiscent of the Good Old Days!

Sent from my iPad

On Jul 9, 2021, at 5:21 PM, Douglas Miller <durga...@gmail.com> wrote:



Interesting project. So, the floppy drive is just decoration? The "media" is some storage device (SD, CF, ...) attached to the Z80? There would be no diskette in the drive - or at least no diskette that contains data? I know the MAME simulators have gone overboard (or not?) with simulating audio, and have a lot of audio clips for floppy drives - maybe just add a speaker (and audio circuitry) and leave the drive dead (except for LED)?


As I recall, the motor might be a bit tricky. But if you only need to approximate RPM then maybe it can be simplified. Just a matter of some analog circuitry. Does head load exist on 5" drives? The ones I remember were always loaded - it was the 8" drives that actually loaded/unloaded the heads. LED should be pretty basic, I presume.


I suppose it doesn't need to actually be a Z80 in the controller, either? Could be an rPi running Linux?



On 7/9/21 3:09 PM, norberto.collado koyado.com wrote:
I started years ago on the idea to modify a bad H17 floppy drive to be controlled by a Z80 controller. The Z80 controller will communicate with the H17 controller, to read/write data to on-board RAM with battery backup. Also, it will control the floppy drive spindle, track zero detector, diskette media detector, and to be able to seek between tracks. 

I have several 5.25" bad floppy drives that I can use. The idea is to have the same feel and look like the original floppy drive. You just insert a floppy diskette and then the Z80 will emulate all floppy conditions. It is more like having the SVD-III controlling a real floppy drive.

The idea for using the Z80 is to use all the H17 code without the need to re-write that much. The goal is for my personal learning on floppy technology especially for the H17 controller as is the easy one to tackle. Also, to keep my H17 enclosure as original.

My question is: How easy is to interface to the floppy cables that controls the motors? I'm looking for a simple circuit design that can spin the floppy media (ignore RPM's), head load, and control the seek operation. The sensors should be easy to do (track Zero and floppy media presence) + drive LED.

This is the floppy drive that I have, and this will be next year project depending on how easy is to interface. I just want to take out the top board and insert the Z80 controller board and plug in the cables.

<DSCF0487__44731.1572898937.jpg>

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Douglas Miller

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Jul 9, 2021, 6:27:42 PMJul 9
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I remember a DEC word processor with 8" drives (PDP-8 I believe) that had virtually no head-load sustain timeout. Talk about a cringe-worthy racket. It sounded terrible. At least HDOS and CP/M kept the head loaded for awhile after an access. Wasn't head-load tied to motor-on?

Dave McGuire

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Jul 9, 2021, 6:35:58 PMJul 9
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On 7/9/21 6:27 PM, Douglas Miller wrote:
> I remember a DEC word processor with 8" drives (PDP-8 I believe) that
> had virtually no head-load sustain timeout. Talk about a cringe-worthy
> racket. It sounded terrible. At least HDOS and CP/M kept the head loaded
> for awhile after an access. Wasn't head-load tied to motor-on?

Yup, VT78, essentially a VT52 terminal with a single-chip PDP-8
(Intersil 6100) on another board mounted inside. We have a pair of them
at LSSM.

-Dave

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Dave McGuire, AK4HZ
New Kensington, PA

norberto.collado koyado.com

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Jul 9, 2021, 7:27:49 PMJul 9
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I want to re-use spare parts that I have such as Z80, 512KB RAM, CF cards, etc. I do not see the need to use a micro as we have a solution for that right now; SVD, GOTEK.

I might work on it after I'm done with all the H8 boards in the pipeline. Also, I need to get back to the Z67-SSD board which has some HW/SW designs problems as it is very unstable when compared with the Z67-IDE+. 

I just want to brainstorm now this crazy idea to get valuable feedback.

Thanks,
Norberto

From: se...@googlegroups.com <se...@googlegroups.com> on behalf of Douglas Miller <durga...@gmail.com>
Sent: Friday, July 9, 2021 3:27 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] H17 Floppy Drive RAW Read/Write Z80 Controller!
 

Mark Garlanger

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Jul 10, 2021, 12:41:54 AMJul 10
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What is the end goal of the setup? Do you want to have these drives simulate in real-time what they would be doing if connected to your H8? If you are going to use the H17 code, you will have to at least do some emulation of the H17 controller (map ports, translate port accesses to signals on the cable, etc.).  And how is the Z80 connected to the floppy drive, going to know what it should be doing at any given point? Have you considered doing something with the cabling coming from the H8, like splitting it to go to both the SVD and the physical drive? 

Mark

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norberto...@koyado.com

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Jul 10, 2021, 3:18:46 AMJul 10
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Good questions Mark. Let me put together a block diagram on what I want to create. The end goal is for learning purposes on how the H17 controller + floppy works. I think more like a companion to the Z67-IDE+ controller. If I can get it to work with the H17 controller, then I can create another board to do the same for the H37.

 

It is a RAW read/write SSD drive. You can format it with the OS and then do reads/writes as needed. I can use the Z80 v4 board to write H8D images to it and to create new H8D images as needed. All images will live on the VDIP1 USB flash drive. At this time I see it more like a Z80 with a lot of RAM and a big battery backup (along with the floppy I/O circuit). Not sure if a CF card or serial ports are needed at this time. A lot of endless possibilities…

 

Norberto

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Mark Garlanger
Sent: Friday, July 9, 2021 9:42 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] H17 Floppy Drive RAW Read/Write Z80 Controller!

 

What is the end goal of the setup? Do you want to have these drives simulate in real-time what they would be doing if connected to your H8? If you are going to use the H17 code, you will have to at least do some emulation of the H17 controller (map ports, translate port accesses to signals on the cable, etc.).  And how is the Z80 connected to the floppy drive, going to know what it should be doing at any given point? Have you considered doing something with the cabling coming from the H8, like splitting it to go to both the SVD and the physical drive? 

image001.jpg

Douglas Miller

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Jul 10, 2021, 7:34:25 AMJul 10
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Thought of one more sound effect you need: stepper motor. More analog circuitry, I believe.

I guess it depends on what has gone wrong with your "bad drives", but do you really need to remove the existing drive electronics? If you just used them to interface to the head load (if present), motor, and stepper motor, that would make things a lot simpler. It would make your Z80 board more universal as well.

Peter Higgins

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Jul 10, 2021, 12:15:47 PMJul 10
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Some thoughts on this project:

Even if your goal is for the floppy drive mechanism to provide the "look and feel" of a functional drive, the drive does need to have functional stepper and spindle motors and a functional head load solenoid. As Douglas pointed out above, if your "bad drive" does not work because one of these two motors or the solenoid has failed, your "bad drive" will not be able to provide the "look and feel" you want to produce.

With specific reference to the Qumetrak 592 you pictured - it uses a 12V direct drive spindle motor. The electronics used to drive the spindle motor (which regulates its speed and turns it on and off) are on a PC board attached directly to the spindle motor. I have several Qumetrak drives that failed because the spindle motor control board has failed. If that happens, you would need to do a board level repair of the spindle driver control board itself in order to get a functional spindle motor. I recall the wires to the motor windings are soldered directly to the control board, and I wouldn't attempt to drive the motor directly without use of its own control board. If your spindle motor assembly works, then interfacing to it is very simple - all it needs is a simple logic-level "motor on" signal.

Driving the Qumetrak 592 head stepper motor will involve the most work. The four windings of the stepper motor are powered from 12V and driven by a pair of 75452 dual high-current output drivers. You could program a Z80 to provide the correct sequence of signals to the drivers for the windings. Alternatively, as Douglas pointed out, if the existing floppy drive logic board (and the motor itself) still work you could just let the existing floppy drive logic board do the work.

The Qumetrak 592 head load solenoid is powered from 12V and driven through one section of a 75452, so that component is easy to control.

As you pointed out, interfacing to the track 0 and index sensors is easy. However, these sensors have also been known to fail and are another cause for a "bad drive".

The Qumetrak 592 manual contains schematics for two versions of this drive, which gives you a pretty good idea for what is involved in controlling this device:

norberto...@koyado.com

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Jul 10, 2021, 3:33:43 PMJul 10
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Thanks Peter for the feedback. I like Douglas’ idea to let the floppy board drive the logic and less work for the Z80 CPU. My definition of a bad floppy drive, is that everything works except the heads. No matter how much I clean the heads I cannot format or read from it. Everything else is functional.

 

Thanks,

Norberto

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Peter Higgins
Sent: Saturday, July 10, 2021 9:16 AM
To: SEBHC <se...@googlegroups.com>
Subject: Re: [sebhc] H17 Floppy Drive RAW Read/Write Z80 Controller!

 

Some thoughts on this project:

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