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Thread: I just bricked a lovely Mostek STD-Bus / MDX boards Development System

  1. #11
    Join Date
    Jan 2007
    Location
    Pacific Northwest, USA
    Posts
    33,074
    Blog Entries
    18

    Default

    Looking at Larry's directory listing, you might be able to restore this thing to a 360K drive--just limit the cylinder count to 40 on the IMD menu. I haven't examined the sample I have in detail--it could be that the client was using 720K 5.25" drives and using only the first 40 cylinders.

    Worth a try, at any rate.

  2. #12
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,311

    Default

    Chuck,
    I'll have a look with 22DISK, to see if my Definition for cpmtools might be in error.
    That a good possibility, since IMDA & IMDU say it's 160 Tracks.

    Code:
    IMageDisk Utility 1.18 / Mar 07 2012
    IMD 1.18: 26/11/2019 18:34:25
    
    Colex 850 Boot disk.  96tpi DSDD 5.25"
    
    Written Dec 26, 2019
    
    CPG
    
    Assuming 1:1 for Binary output
     0/0 300 kbps DD  10x512
          1   2   3   4   5   6   7   8   9   10 
          D   D   D   D   D   D   D   D   D00 D00
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          DE5 DE5 DE5 DE5 DE5 DE5 DE5 DE5 DE5 DE5
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    79/0  1   2   3   4   5   6   7   8   9   10 
          D   D   DE5 D   D   DE5 D   D   DE5 DE5
    79/1  12  13  14  15  16  17  18  19  20  11 
          D   D   D   D   D   D   D   D   D   D  
    160 tracks(80/80), 1600 sectors (250 Compressed)
    One way or another I'll get to the files. More a bit later.

    Larry

  3. #13
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    Default

    Larry, you should have a ZIP archive of the files sent to both you and the OP by now. Check your PMs.

  4. #14

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    Going down the rabbit hole a bit further, I've tried writing some 360 K floppies using ImageDisk on an old 486 PC that has a good 360 K floppy drive, but now I'm stuck wondering if my Mostek FDD and FDC are even setup or working correctly, because I'm getting read errors no matter what disk I put in the drive.

    I'll include some photos here. First I'll show you the alternate settings I used to try to write your Colex850 image (basically just setting it to single-step and to go from 300 kbs to 250 kbs). It wrote as much as it could to the disk successfully, and I was hoping the Mostek would at least boot what was there.

    The next image shows the read errors (though not all hope is lost, when I disconnect the floppy drive, the hard drive boots to its "missing cpm3.sys" error message, and when I connect the floppy drive, it does appear to be trying to boot the floppy disk, and I get the read error shown).

    IMG_1227.jpg

    IMG_1229.jpg

    IMG_1228.jpg

    Next are some photos of the bizarre ribbon cable that is attached from the FDC (a 50 pin male port) to the FDD (a 17-pin edge connector). It was definitely hacked together - is this a standard cable? I should probably buy a manufactured one, as this could certainly be part of the problem. The original owner of the machine, who received it directly from Mostek while he worked there as a developer, said he never actually used the 5.25" drive and always used the external 8" floppy drive.


    IMG_1219.jpg

    IMG_1223.jpg

    IMG_1224.jpg

    I wonder if I could hook up the 8" floppy drive to my PC and use ImageDisk to write a bootable 8" floppy? I at least know that drive works and the controller can read from it successfully.

  5. #15
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    Quote Originally Posted by dvanaria View Post
    IMG_1219.jpg

    IMG_1223.jpg

    IMG_1224.jpg

    I wonder if I could hook up the 8" floppy drive to my PC and use ImageDisk to write a bootable 8" floppy? I at least know that drive works and the controller can read from it successfully.
    Your 5.25" FD ribbon cable is reminiscent of the ones to IBM PS/2 3.5" ones. Anyway, I'd guess that is definitely a source of your problem, as the 50-pin FDC-out isn't mapped in any way I recognise for the PS/2 3.5" edge-connector drives, which use a 40-way card-edge, to include power supply. Your card-edge connector is 2 x 17-pin (i.e. 34-pin), so std. floppy drive, but FDC 29 to FD 1 is non-standard in the extreme. It just *might* be for a PS/2 Model 50 3.5" edge-connector drive, where FD 1 is "2nd drive installed", However FDC 29 is supposed to be a Ground line, so the FDC 50-pin connector's pin-out to signal needs more research.

  6. #16
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    I was sure I had a wiring Diagram of the 50 Conductor to the 34 Conductor layout.
    But I can't find it for the moment.

    Looking at the 50 Pin layout here I'm thinking that
    the actual conductor that goes from Pin 30 is connected to Pin 2 of the 34 Pin Connector. That would make sense
    because Pin 2 on the 34 Pin Connector is /REDWC.

    I'm thinking the actual wiring shown in the Photo is:
    Code:
    50 Pin connector Pin 30 to 34 Pin Connector Pin 2 (/REDWC from FDC to Floppy)
    50 Pin Connector Pin 32 is cut  (Head Select prevented from FDC)
    50 Pin connector Pin 34 is cut  (Disk Changed/Disk Ready prevented to FDC)
    A quick test with an OHM Meter would prove that the conductor layout is (Right to Left) Even Odd
    as in 2 1, 4 3, 6 5,.......

    Larry
    Last edited by ldkraemer; November 28th, 2019 at 06:10 AM.

  7. #17
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    Quote Originally Posted by ldkraemer View Post
    I was sure I had a wiring Diagram of the 50 Conductor to the 34 Conductor layout.
    But I can't find it for the moment.

    Looking at the 50 Pin layout here I'm thinking that
    the actual conductor that goes from Pin 30 is connected to Pin 2 of the 34 Pin Connector. That would make sense
    because Pin 2 on the 34 Pin Connector is /REDWC.

    I'm thinking the actual wiring shown in the Photo is:
    Code:
    50 Pin connector Pin 30 to 34 Pin Connector Pin 2
    50 Pin Connector Pin 32 is cut
    50 Pin connector Pin 34 is cut
    Ahh, OK, my bad. I've corrected your first link above, it had "http://https://" prefixes, only the 2nd is needed.

    Pin 32 being cut doesn't seem right, if 8" drives are DS1 and DS2, then 5.25" drives would be DS3 and DS4, I guess, or vice versa.
    Pin 34 being cut doesn't seem right either (Step Direction IN/OUT)

    Quote Originally Posted by ldkraemer View Post
    A quick test with an OHM Meter would prove that the conductor layout is (Right to Left) Even Odd
    as in 2 1, 4 3, 6 5,.......

    Larry
    Yet again, Ahhh. That seems weird to me. Ribbon filaments are numbered 1-34, or however many, from the (later common) red stripe end (Pin 1).

    The cable makeup seems just wrong. Maybe the card-edge 34-way connector was crimped the wrong way around, or the 50-pin FDC end?

  8. #18
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    A quick follow-up, how is the drive jumpered? Drive 1, 2, 3 or 4?

  9. #19
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    Darron,
    tried writing some 360 K floppies using ImageDisk on an old 486 PC that has a good 360 K floppy drive
    The problem with this is the Track for a 360 is too wide, and by single stepping you are constantly overwriting part
    of the tracks as you write. If you have a 5.25" 1.2 M Floppy drive give it a try using it. The 1.2 M floppy drive has a
    thinner track width.

    Do you have a Schematic of the Floppy Disk Controller's wiring?

    Thanks.

    Larry

  10. #20
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    Darron, the MDX-FLP Controller Document is on Bitsavers:

    The wiring should be:

    Code:
    	MDX-FLP
    2	
    4	
    6	
    8	
    10	
    12	
    14	Side Select
    16	Side Select
    18	Head Load
    20	8” Index
    22	Drive Ready
    24	5” Index
    26	Drive Select 0
    28	Drive Select 1
    30	Drive Select 2
    32	Drive Select 3
    34	Direction
    36	Step
    38	Write Data
    40	Write Gate
    42	Track 0
    44	Write Protect
    46	Read Data
    48	
    50

    Larry

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