Rocky Gush Floppy Drive Interface



  • edited May 2013
    Ok, no problem, when you can, do it, many thanks again.
  • edited May 2013
    Hi flopping

    I have put together the following to assist you with the assembly of the interface. Just a few notes first:

    1. The two pdf files is the component layout with and without the pads.

    [URL="http:\\\Construction\Component values layout.pdf"]http:\\\Construction\Component values layout.pdf[/URL]
    [URL="http:\\\Construction\Component values with pads.pdf"]http:\\\Construction\Component values with pads.pdf[/URL]

    2. Only use TTL 74LSXXX chips and not the CMOS versions, i.e. 74HCXXX. The interface was designed around the TTL voltage and logic levels. I tried the C and HC range myself and it does not work. The same for the EPROMS, use 2764, 27128 and not 27C64 or 27C128.

    3. The LED (D7) is in series with the VCC of U11 (74LS164) and acts a supply voltage dropper. When the interface was built in the middle 80?s, Rocky found that U11 was switching to fast and was corrupting the data to the printer. To compensate for this, he dropped the supply voltage to the chip with the LED and the problem was solved.

    4. The R16/C3 mod between two gates of U10 is there to filter out noise on the data line of the floppy drive. On the original board, Rocky soldered the resistor and cap on top of the IC. I soldered them onto the bottom of the board. See pictures.

    Cap and transistor mod old board.jpgCap and transistor mod new board.jpg

    5. Diode D8 ( 1N4148 ) is soldered onto the collector of transistor Q1 (BCY65E, I used a 2222A) and the combination is then soldered onto the board. See picture.

    transistor and diode.JPG

    6. Remember the two jumpers as on the Picture.
    7. If you would like to add the outgoing edge connector to connect other peripherals on the interface (e.g. joystick interface, etc), then note that A14 and/ROMCS line to the outgoing edge connector does not go straight through as with the other, but must go to the pads in the centre between the outside of the edge connector pads. See picture .
    8. IC12 is soldered under IC13 within the IC socket. Depending of the size of the plastic support of the 28 Pin socket, you may have to cut the support plastic on the pin 14/15 side. The support in the middle must be cut to accommodate IC12. See pictures .


    9. Originally (in the 80?s) I used two 360K/5.25 double height floppy drives, which was in an external case with a power supply. With my new construction, I build a 1.44/3.5 drive inside of my case. See picture. It is a Sony model MPF920. The ribbon cable is a one to one configuration between the two plugs.

    10. Each side of the disk is seen as a separate drive by the interface. The FD1791 can connect to 4 drives, each double sided (Edge connector pin 10,12,14,6) . The interface recognise every side of the disk drive as a separate drive, thus if you connect four physical drive to the interface, you will see 8 drives when the interface initialise ( 0&4, 1&5, 2&6, 3&8 ). With the one to one cable configuration (as in my case) on the new drive types, the Drive 1 line of the interface is connected to the drive. This results in a boot message of drives 1&5. If you would like to see 0&4 if you use one drive, then you will have to swap Drive 0 and Drive 1 wires on the cable (12 and 14). Older drives had 4 drive selectors, where the newer ones can only select two. With the original drives, all four drives were on a one to one cable and each drive was selected on-board with either a jumper or DIP switch as drive 1 to 4.

    11. The floppy controller chip does not recognise the double density line from the drive, resulting in that you can use 80 tracks per side single density. I formatted it to 82 tracks I think, resulting in 400K per side. It was not necessary for me to mod the drive to disable the single/double detection circuit, but may be a problem with certain manufacturers or drive models. This is in most cased a LED and photo transistor at the front of the drive controller board.

    12. The printer interface is designed to work with an Epson Compatible printer. I currently use a LQ-870. The cable is also a one to one between the two plugs.

    13. I have mounted my Issue 2/48k board, a small motherboard with two edge connectors, Kempston joystick interface that plugs onto the small motherboard, Rocky Gush interface, Disc Drive and power supply in an old Olivetti terminal case. See picture.



    Final Pictures of board. Note that I have not soldered the outgoing edge connector on yet.



    I hope this will assist you and good luck with the construction. Please let me know if you need more information or if you get stuck somehow.

  • edited May 2013
    Ok, Pierre, thank you very much for the detailed information, i will go to mount and i will tell you the results.

    PD: One more question, i have a mistake, the floppy IC controller are the FD1791 and i have the IC?s FD1771, are compatibles? or i need to get the IC FD1791?
  • edited May 2013

    As far as I know, the only difference is that the 1771 is only single density and the 1791 can do single and double density. I think the DOS should be able to work.

  • edited May 2013
    But the 1771 are 28 pin and the 1791 are 40 pin, and both works with single and double density.
  • edited May 2013
    Hi flopping

    I am not sure where you got your info from, but according to my data sheets, they are both 40pin devices. See datasheets below. Pin 37 on the 1791 is /DDEN, which selects single or double density. Pin 37 on the 1771 is /DINT, which is the disk initialisation input. After looking at the Gush circuit diagram, pin 37 is at logic "0", which means it is switched to double density. Pin 37 on the 1771 must also be at logic "0" to be initialised. I am not sure how the DOS will handle the 1771, but it will be worth a try. Digital FD1771.pdf Digital FD179X.pdf

    See Also the MB88XX data sheet. It is an aftermarket chip, which is compatible with the 179X range. The only difference is that it does not need the +12v on Pin 40. You will see that Pin 40 is not used on the datasheet. The MB8866 is compatible with the 1791

    Hope this will help

  • edited May 2013
    You are rigth, Pierre, i have a mistake again, i was thinking that the series of IC 1770, 1171 and 1772 are similar caracteristiques and with the same pins, but no, the 1771 are 40 pins and the 1772 only 28 pins and i have the IC 1772.

    Do you think that this chips are equivalent or similar that 1791?, maybe i can put this chip in the circuit, but modify a bit the eschematic, or maybe not posible?, many thanks for you help.
  • edited May 2013
    Hi flopping

    If you had a 1771, it would have being worth a try to pop it into the socket and see if it would work. I am quite confident that it should, but am purely guessing. The datasheets states that it is backward compatible. The 1793 and the 1791 only differs with the data bus, which is inverted with the 1791. If you add inverters on the data bus, the 1793 should work. The 1793 was also used with the TRS80 range of computers.

  • edited May 2013
    Ok, many thanks again Pierre.

    Anybody can tell me where i can buy the chips FD1791?
  • edited May 2013
    Hi flopping

    The controller chips are not manufactured anymore as far as I know. There are a few advertised on eBay currently. The prices range from $14 to $35. Best will be to Google or put in an offer on one of the eBay units.

  • anyone have a copy of documents mentioned earlier in this topic ? (schematics and manual).
    all the links is dead and doesn't have a copy of them.
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