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S100 Floppy Controller

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  • danlb_2000
    A while back I posted about an IMSAI 8080 system I acquired and my efforts to get it back into working order. The system contains a floppy controller that I
    Message 1 of 19 , Mar 16, 2014
      A while back I posted about an IMSAI 8080 system I acquired and my efforts to get it back into working order. The system contains a floppy controller that I have not been able to identify, so I decided to reverse engineer it and document my findings. I have put together a page that contain pictures of the board, schematics that I generated and a dump of the boot ROM.
    • s100doctor
      http://atarihq.com/danb/s100Floppy.shtml http://atarihq.com/danb/s100Floppy.shtml Nice work. I emailed you privately about the Web page and some notes on the
      Message 2 of 19 , Mar 16, 2014

        http://atarihq.com/danb/s100Floppy.shtml

        Nice work. I emailed you privately about the Web page and some notes on the source code. Contact me if you didn't get that, I'm experimenting with how I access this Yahoo group.

        Herb Johnson
        retrotechnology.com

      • dfnr2
        Nice! It must be an early vintage (1975-1977) controller for 8 drives. Dave
        Message 3 of 19 , Mar 17, 2014
          Nice!  It must be an early vintage (1975-1977) controller for 8" drives.
          Dave
        • Systems Glitch
          ... Interesting! Ohio Scientific took the same approach with their floppy system, using a UART to encode/decode the datastream. In their case it was a Motorola
          Message 4 of 19 , Mar 17, 2014
            > A while back I posted about an IMSAI 8080 system I acquired and my efforts to get it back into working order. The system contains a floppy controller that I have not been able to identify

            Interesting! Ohio Scientific took the same approach with their floppy system, using a UART to encode/decode the datastream. In their case it was a Motorola 6850.

            > http://atarihq.com/danb/s100Floppy.shtml http://atarihq.com/danb/s100Floppy.shtml

            Your image links are broken -- looks like there's a backslash in the path where there should be a forward slash.

            Thanks,
            Jonathan
          • Dave McGuire
            ... Heath did the same with the H-17 floppy subsystem for the H-8. I ve always thought it was a bit, erm, lowbrow , but it works. -Dave -- Dave McGuire,
            Message 5 of 19 , Mar 17, 2014
              On 03/17/2014 02:28 PM, Systems Glitch wrote:
              >> A while back I posted about an IMSAI 8080 system I acquired and my
              >> efforts to get it back into working order. The system contains a
              >> floppy controller that I have not been able to identify
              >
              > Interesting! Ohio Scientific took the same approach with their floppy
              > system, using a UART to encode/decode the datastream. In their case
              > it was a Motorola 6850.

              Heath did the same with the H-17 floppy subsystem for the H-8. I've
              always thought it was a bit, erm, "lowbrow", but it works.

              -Dave

              --
              Dave McGuire, AK4HZ
              New Kensington, PA
            • Dave McGuire
              ... Yes it does. But on the other hand, banging up a UART and a microcontroller (if the usual on-chip UARTs won t do the required stuff) would be pretty easy.
              Message 6 of 19 , Mar 17, 2014
                On 03/17/2014 03:54 PM, Systems Glitch wrote:
                >> Heath did the same with the H-17 floppy subsystem for the H-8. I've
                >> always thought it was a bit, erm, "lowbrow", but it works.
                >
                > It certainly makes attempting to deal with the disks nowadays an interesting task!

                Yes it does. But on the other hand, banging up a UART and a
                microcontroller (if the usual on-chip UARTs won't do the required stuff)
                would be pretty easy.

                Actually, I think that'd be a fun project.

                -Dave

                --
                Dave McGuire, AK4HZ
                New Kensington, PA
              • Systems Glitch
                ... It certainly makes attempting to deal with the disks nowadays an interesting task! Thanks, Jonathan
                Message 7 of 19 , Mar 17, 2014
                  > Heath did the same with the H-17 floppy subsystem for the H-8. I've
                  > always thought it was a bit, erm, "lowbrow", but it works.

                  It certainly makes attempting to deal with the disks nowadays an interesting task!

                  Thanks,
                  Jonathan
                • Paul Birkel
                  What controller brow was IBM using when they originally introduced the floppy disk drive with S/370? Curious ...
                  Message 8 of 19 , Mar 17, 2014
                    What controller "brow" was IBM using when they originally introduced the "floppy disk" drive with S/370?  Curious ...



                    On Mon, Mar 17, 2014 at 3:43 PM, Dave McGuire <Mcguire@...> wrote:
                     

                    On 03/17/2014 02:28 PM, Systems Glitch wrote:
                    >> A while back I posted about an IMSAI 8080 system I acquired and my
                    >> efforts to get it back into working order. The system contains a
                    >> floppy controller that I have not been able to identify
                    >
                    > Interesting! Ohio Scientific took the same approach with their floppy
                    > system, using a UART to encode/decode the datastream. In their case
                    > it was a Motorola 6850.

                    Heath did the same with the H-17 floppy subsystem for the H-8. I've
                    always thought it was a bit, erm, "lowbrow", but it works.

                    -Dave

                    --
                    Dave McGuire, AK4HZ
                    New Kensington, PA


                  • B Degnan
                    ... From: Paul Birkel To: midatlanticretro Sent: Mon, Mar 17, 2014 3:56 pm Subject: Re:
                    Message 9 of 19 , Mar 17, 2014

                      -----Original Message-----
                      From: Paul Birkel <pbirkel@...>
                      To: midatlanticretro <midatlanticretro@yahoogroups.com>
                      Sent: Mon, Mar 17, 2014 3:56 pm
                      Subject: Re: [midatlanticretro] S100 Floppy Controller



                      On Mon, Mar 17, 2014 at 3:43 PM, Dave McGuire <Mcguire@...> wrote:
                       
                      On 03/17/2014 02:28 PM, Systems Glitch wrote:
                      >> A while back I posted about an IMSAI 8080 system I acquired and my
                      >> efforts to get it back into working order. The system contains a
                      >> floppy controller that I have not been able to identify
                      >
                      > Interesting! Ohio Scientific took the same approach with their floppy
                      > system, using a UART to encode/decode the datastream. In their case
                      > it was a Motorola 6850.

                      Heath did the same with the H-17 floppy subsystem for the H-8. I've
                      always thought it was a bit, erm, "lowbrow", but it works.

                      -Dave

                      --
                      Dave McGuire, AK4HZ
                      New Kensington, PA


                      > What controller "brow" was IBM using when they originally introduced the "floppy disk" drive with S/370?  Curious ...

                      I think it's easy to apply today's perspective and knowledge to yesterday's problems.  It's an evolution more so than skill/brow don't you think?


                    • Dave McGuire
                      ... It definitely is, but when the H-17 was developed, there were several floppy controller ICs available. They were just expensive. ;) Most other companies
                      Message 10 of 19 , Mar 17, 2014
                        On 03/17/2014 04:16 PM, B Degnan wrote:
                        > >> A while back I posted about an IMSAI 8080 system I acquired and my
                        > >> efforts to get it back into working order. The system contains a
                        > >> floppy controller that I have not been able to identify
                        > >
                        > > Interesting! Ohio Scientific took the same approach with their floppy
                        > > system, using a UART to encode/decode the datastream. In their case
                        > > it was a Motorola 6850.
                        >
                        > Heath did the same with the H-17 floppy subsystem for the H-8. I've
                        > always thought it was a bit, erm, "lowbrow", but it works.
                        >
                        >
                        >> What controller "brow" was IBM using when they originally introduced
                        > the "floppy disk" drive with S/370? Curious ...
                        >
                        > I think it's easy to apply today's perspective and knowledge to
                        > yesterday's problems. It's an evolution more so than skill/brow don't
                        > you think?

                        It definitely is, but when the H-17 was developed, there were several
                        floppy controller ICs available. They were just expensive. ;) Most
                        other companies (as you know) used 'em.

                        -Dave

                        --
                        Dave McGuire, AK4HZ
                        New Kensington, PA
                      • Dave McGuire
                        ... Very true, but the FD1771 was introduced in 1976...two years before the Heath H-17...the use where I suggested it was a bit lowbrow . -Dave -- Dave
                        Message 11 of 19 , Mar 17, 2014
                          On 03/17/2014 05:31 PM, retro wrote:
                          > A number of posts, suggest that using a UART as a floppy controller in
                          > early microcomputers was various flavors of unnecessary. The facts are,
                          > that early microprocessors came before single-chip floppy controllers,
                          > and floppy drives were around before say the Intel 8080 processor.
                          >
                          > Many of the earliest floppy disk controllers - including for and by
                          > IMSAI and MITS Altair - were made from either TTL chips with or without
                          > UARTS, or very early fast microcoded TTL designs, or themselves used the
                          > earliest microprocessors or microcontrollers. And a whole generation of
                          > floppy controllers were hard-sectored, because that was simpler to
                          > manage with such technology.
                          >
                          > This is ground I covered a few years ago:
                          >
                          > http://www.retrotechnology.com/dri/first_floppy.html
                          >
                          > There were a generation of floppy controllers before single-chip FDC's
                          > were available. That was simply the available technology. No shame or
                          > shortchange in that.

                          Very true, but the FD1771 was introduced in 1976...two years before
                          the Heath H-17...the use where I suggested it was a bit "lowbrow".

                          -Dave

                          --
                          Dave McGuire, AK4HZ
                          New Kensington, PA
                        • Bill Sudbrink
                          The blue die job on the PCB might suggest Solid State Music as the manufacturer. From: midatlanticretro@yahoogroups.com
                          Message 12 of 19 , Mar 17, 2014

                            The blue die job on the PCB might suggest Solid State Music as the manufacturer.

                             

                            From: midatlanticretro@yahoogroups.com [mailto:midatlanticretro@yahoogroups.com] On Behalf Of danlb_2000@...
                            Sent: Sunday, March 16, 2014 6:56 PM
                            To: midatlanticretro@yahoogroups.com
                            Subject: [midatlanticretro] S100 Floppy Controller

                             



                            A while back I posted about an IMSAI 8080 system I acquired and my efforts to get it back into working order. The system contains a floppy controller that I have not been able to identify, so I decided to reverse engineer it and document my findings. I have put together a page that contain pictures of the board, schematics that I generated and a dump of the boot ROM.





                            No virus found in this message.
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                          • Systems Glitch
                            ... Certainly -- OSI s 6850 based FDC was certainly easier to troubleshoot than the all-TTL North Star controller. Also, I don t think I ve had any controller
                            Message 13 of 19 , Mar 17, 2014
                              > There were a generation of floppy controllers before single-chip FDC's
                              > were available. That was simply the available technology. No shame or
                              > shortchange in that.

                              Certainly -- OSI's 6850 based FDC was certainly easier to troubleshoot than the all-TTL North Star controller. Also, I don't think I've had any controller failures among my OSI and North Star controllers...

                              Thanks,
                              Jonathan
                            • Systems Glitch
                              ... My original thought as well, but the board doesn t have any of their usual markings. Not that the absence of marking means anything definite. Thanks,
                              Message 14 of 19 , Mar 17, 2014
                                > The blue die job on the PCB might suggest Solid State Music as the
                                > manufacturer.

                                My original thought as well, but the board doesn't have any of their usual markings. Not that the absence of marking means anything definite.

                                Thanks,
                                Jonathan
                              • retro
                                A number of posts, suggest that using a UART as a floppy controller in early microcomputers was various flavors of unnecessary. The facts are, that early
                                Message 15 of 19 , Mar 17, 2014
                                  A number of posts, suggest that using a UART as a floppy controller in
                                  early microcomputers was various flavors of unnecessary. The facts are,
                                  that early microprocessors came before single-chip floppy controllers,
                                  and floppy drives were around before say the Intel 8080 processor.

                                  Many of the earliest floppy disk controllers - including for and by
                                  IMSAI and MITS Altair - were made from either TTL chips with or without
                                  UARTS, or very early fast microcoded TTL designs, or themselves used the
                                  earliest microprocessors or microcontrollers. And a whole generation of
                                  floppy controllers were hard-sectored, because that was simpler to
                                  manage with such technology.

                                  This is ground I covered a few years ago:

                                  http://www.retrotechnology.com/dri/first_floppy.html

                                  There were a generation of floppy controllers before single-chip FDC's
                                  were available. That was simply the available technology. No shame or
                                  shortchange in that.

                                  --
                                  Herbert R. Johnson
                                  http://www.retrotechnology.com OR .net
                                • bobk2ut
                                  And the UART was far more advanced than an Apple disk controller; all the serialization and track stepper control was done in software! Bear in mind how
                                  Message 16 of 19 , Mar 18, 2014
                                    And the UART was far more advanced than an Apple disk controller; all the serialization and track stepper control was done in software!

                                    Bear in mind how expensive an FDC was back then compared to other chips.  It was probably hard for engineers to justify using such expensive devices.  If the floppy controller board cost $200 to make but needed only 500 hours of software work, versus $40 in parts and 2000 hours of software, usually the latter won.  Been there, done that with having LEDs rejected from a design because of the cost of the two resistors and two LEDs!

                                    Bob
                                  • Paul Birkel
                                    Which is why I wondered about the IBM brow-ness :- . Surely using a UART was a step up from discrete TTL (if that s what was the original IBM S/370-era
                                    Message 17 of 19 , Mar 18, 2014
                                      Which is why I wondered about the IBM brow-ness :->.  Surely using a UART was a step "up" from discrete TTL (if that's what was the original IBM S/370-era implementation)!


                                      On Tue, Mar 18, 2014 at 7:42 AM, <bob@...> wrote:
                                       

                                      And the UART was far more advanced than an Apple disk controller; all the serialization and track stepper control was done in software!

                                      Bear in mind how expensive an FDC was back then compared to other chips.  It was probably hard for engineers to justify using such expensive devices.  If the floppy controller board cost $200 to make but needed only 500 hours of software work, versus $40 in parts and 2000 hours of software, usually the latter won.  Been there, done that with having LEDs rejected from a design because of the cost of the two resistors and two LEDs!

                                      Bob


                                    • Systems Glitch
                                      ... Well, IBM won out on becoming standard, for as standard as anything was then. Therefore they /must/ have had the best design/format, right?! Thanks,
                                      Message 18 of 19 , Mar 18, 2014
                                        > Which is why I wondered about the IBM brow-ness :->. Surely using a UART
                                        > was a step "up" from discrete TTL (if that's what was the original IBM
                                        > S/370-era implementation)!

                                        Well, IBM won out on becoming "standard," for as standard as anything was then. Therefore they /must/ have had the best design/format, right?!

                                        Thanks,
                                        Jonathan
                                      • retro
                                        The points below are: a UART as a step up from TTL designs; and the cost/benefits decision about using cheaper parts but more development time. There were a
                                        Message 19 of 19 , Mar 18, 2014
                                          The points below are: a UART as a step "up" from TTL designs; and the
                                          cost/benefits decision about using cheaper parts but more development time.

                                          There were a lot of kitchen-table companies producing lots of kinds of
                                          microcomputer products through the 1970's. S-100 and other "bus"
                                          architectures made it even easier, to just produce a PC board and not a
                                          whole desktop computer. At any time, any new company (person at a
                                          kitchen table) could produce a "latest and greatest" product. But old
                                          companies had old inventory, and a base of users with that old technology.

                                          The common catchphrase in the era was "to decide when you are going to
                                          waste your money", as what was new today would be old and cheaper
                                          tomorrow. But you had to buy something, to participate at all.

                                          So, while any one company would make one, or two generations of floppy
                                          controller; the impression of the era was of rapid change, because LOTS
                                          of companies followed EACH OF the trends. FDC chipsets became standard
                                          (later) because the chipsets did all the work for any new design.

                                          But old designs, already paid for, still producing revenue, did fine for
                                          years, until those customers found it convenient (eventually necessary)
                                          to buy a "new" computer. That often took years.

                                          Put another way: a response to "you could have made a more advanced
                                          design" is "but I made something rather than delay, and made money, and
                                          helped my customers". It's not always true, of course, in individual
                                          cases; but it's true in the aggregate, given the conditions I've mentioned.

                                          Herb Johnson

                                          On 3/18/2014 6:50 AM, Paul Birkel wrote:
                                          > Which is why I wondered about the IBM brow-ness :->. Surely using a
                                          > UART was a step "up" from discrete TTL (if that's what was the original
                                          > IBM S/370-era implementation)!
                                          >
                                          >
                                          > bob applegate wrote:
                                          >
                                          > And the UART was far more advanced than an Apple disk controller;
                                          > all the serialization and track stepper control was done in software!
                                          >
                                          > Bear in mind how expensive an FDC was back then compared to other
                                          > chips. It was probably hard for engineers to justify using such
                                          > expensive devices. If the floppy controller board cost $200 to make
                                          > but needed only 500 hours of software work, versus $40 in parts and
                                          > 2000 hours of software, usually the latter won. Been there, done
                                          > that with having LEDs rejected from a design because of the cost of
                                          > the two resistors and two LEDs!
                                          >
                                          > Bob
                                          --
                                          Herbert R. Johnson
                                          http://www.retrotechnology.com OR .net
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