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5.25 and 3.5 on the same cable

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    5.25 and 3.5 on the same cable

    Hello all,

    I'm new on this forum. I did a search on my subject but got no match.

    Here is my problem: I am in the process of restoring an Amstrad PC 1512 (XT class, 8086 at 10 MHz). I've managed to install an ST-225 20MB drive salvaged from a no more working IBM, re-low-level formated it (it was a long time I hadn't used Debug...) and found images of the original install disks. I've managed to copy these images to the hard disk (by shutting off the IDE controler of an old Pentium PC and stuck the MFM controler in the ISA bus - to my amazement it did work!

    Now, to ease data transfer, I'd like to convert the pentium (it's a Packard Bell) to a machine with hard disc, DVD ROM, 3.5 and 5.25 floppy. And there is the problem: I have a cable that has three connectors: from the motherboard connector you get: a 3.5" connector, a 5.25 connector, then the twisted cable and another 3.5" connector.

    I don't manager to get both drives working: I set the 3.5 as A: (1.44MB) and the 5.25 as B: in the BIOS. That way, I can access the 5.25, format floppies and read/copy files. The 3.5 however does not work (tells me drive not ready). If I disconnect the 5.25 the 3.5 works (note that I have to physically disconnect it, just disabling in the BIOS does not work.

    So my machine more or less does the job, but I have to alternatively connect or disconnect the 5.25. Am I missing sometĥing ? I've spotted a cable on ebay with the IDC connector _after_ the twist, could this solve my problem? The 3.5 drive has no jumper visible, and the 5.25 has only one that seems to define if first or second drive (I can only access the floppies if I set it to second, at least on my cable.

    Any advice is welcome,

    Thierry

    #2
    1. Both drives need to be set to the second drive select (e.g. DS1, not DS0--but be careful--some older drives have DS1 as the first)
    2. Cabling Motherboard->Drive B->twist->Drive A
    Reach me: vcfblackhole _at_ protonmail dot com.

    Comment


      #3
      Welcome to these forums.

      Drive termination is also important. Terminate per the diagram at [here].

      Originally posted by tcoulon View Post
      The 3.5 drive has no jumper visible ...
      Some 3.5" diskette drives designed for PCs are hardwired to the second drive-select position.

      Comment


        #4
        Originally posted by modem7 View Post
        Welcome to these forums.

        Drive termination is also important. Terminate per the diagram at [here].
        THank you for this information - I think that may be the clue (I remebered temination for SCSI but not for floppies). However, as close as I inspected the drive I can't find anything like a terminator (at least a removable one)- There are four positions I can put a jumper on (labeled DS0 to DS4). DS1 clearly makes it drive A, DS1 works as drive B (but with A unreadable). DS2 and DS3 did not seem to work differently from DS1.

        Looking for information about teh drive (QUMETRAK 142) I was pointed to this information:
        "The IBM PC floppy disk drive bus includes the facility for up to four drives to be daisy-chained, with device addressing being controller by pins 6, 10, 12 and 14.
        Initially, jumpers were used to manually select the device ID (0 through 3) with a flat ribbon cable.
        Another option is a 'twisted' ribbon cable, where the cables serving pins 6 to 14 are reverse between the first and sector drive connector, thereby providing 'cable select' addressing for two devices (only). Using this method, both drives should be jumpered to drive 1 (DS1), with the drive connected to the first (untwisted) connector being drive 1, and the drive connected to the second (twisted) connector being drive 0 (DS0)."

        So, _Another_ seems to mean that you can't have both. I understand this as meaning I should _not_ use the twisted part. I do have an untwisted cable, but it requires a "flat" connector on the floppy controler. So I guess I should connect the 3.5 on the second connector, before the 5.25, set the 360K as A and the 3.5 as B, but none of my 3.5 floppies seems to accept to work that way...

        I guess I have to search for an untwisted cable (if it exists) or live with my plug/unplug system.

        thanks anyway,

        Thierry

        Comment


          #5
          It's possible that your cable is damaged. I had a similar issue and it turned out to be a bad cable.

          Twisted vs untwisted cable is not going to make a difference. The twist just changes DS1 to DS0 on the last drive. They were introduced for ease of assembly, so all floppies could be set to DS1 and the position on the cable would set the drive letter.

          Normally you would set both drives to DS1, put the 5.25 on the middle connector and the 3.5 on the end connector. In the BIOS set A to 3.5 and B to 5.25. I think this was your original setup.

          If this is not working, possibly there is a termination problem. Put the 3.5 in the middle and the 5.25 on the end. In the BIOS set A to 5.25 and B to 3.5.

          If that doesn't work either, try another cable.

          Comment


            #6
            A service manual for the QumeTrak 142 is available from here. To quote from the service manual:

            TERMINATOR

            The input line terminator is a 150 Ohm DIP resistor module which is at the
            factory plugged into the DIP socket, location RNl, on the P,CB. This
            terminator must be present in a single drive, or in the last drive of a daisy
            chain.

            Comment


              #7
              Originally posted by Malc View Post
              The input line terminator is a 150 Ohm DIP resistor module which is at the
              factory plugged into the DIP socket, location RNl, on the P,CB
              Thanks, with your information I found it (I had not expected a chip that big). however removing it does not change anything, so I'll try another cable. I'll tell the result when it arrives.

              Regards

              Comment


                #8
                Well, I did find a PC1512 reference online and discovered something interesting. I was mislead by your characterization of "XT compatible". The Amstrad is very close, but not totally compatible. One key issue is that if motherboard link LK8 is installed, pin 34 READY is used. This is not what the IBM 5160/5150 do. So if LK8 is installed, remove it. Otherwise, you'll get a bunch of "Drive not ready" errors on 1.2 and 1.44 drives, which use this line as a "disk changed" signal.

                Most 3.5" drives have integral "weak" terminators (usually about 1-2K), which should be sufficient for your application. It's not important that the 5.25" drive have them.
                Reach me: vcfblackhole _at_ protonmail dot com.

                Comment


                  #9
                  Originally posted by tcoulon View Post
                  Looking for information about teh drive (QUMETRAK 142) I was pointed to this information:
                  "The IBM PC floppy disk drive bus includes the facility for up to four drives to be daisy-chained, with device addressing being controller by pins 6, 10, 12 and 14.
                  Initially, jumpers were used to manually select the device ID (0 through 3) with a flat ribbon cable.
                  Another option is a 'twisted' ribbon cable, where the cables serving pins 6 to 14 are reverse between the first and sector drive connector, thereby providing 'cable select' addressing for two devices (only). Using this method, both drives should be jumpered to drive 1 (DS1), with the drive connected to the first (untwisted) connector being drive 1, and the drive connected to the second (twisted) connector being drive 0 (DS0)."
                  The floppy cable situation with the IBM PC is shown at [here]. The twist also affects the 'motor on' signals. The drives are configured to only turn their spindle motors based on the state of the 'motor on' line.

                  So, that is the situation with the IBM PC, however, whilst a lot of clones use the same mechanism, some do not. Some use a flat cable, with one drive set to DS0 and the other to DS1, and each drive is configured to turn its spindle motor when the drive is selected.

                  Member vwestlife discovered that his PIII Compaq DeskPro used a similar mechanism to the IBM PC, except that the 'twist' had already been done on the motherboard. So a flat cable is used for a single drive. And a twisted cable used for two drives, however, because two twists are in place, the situation is like the bottom cable in the diagram at [here]. That results in B: being at the end of the cable, and A: in the middle,

                  Ideally, to save time, a member of these forums with a PC1512 will categorically state that the two-drive situation in the PC1512 is xxxxxxxxxxxxxxxx.

                  The earlier thread at [here] indicates that the PC1512 has a flat cable that is soldered to the motherboard.

                  Comment


                    #10
                    I finally located the PC512 service manual. Modem7 is connect--the floppy hookup is not the same as the PC XT--it's the "flat" cable (when the motor line is activated, both motors go on). Beats the devil out of me why the port mapping calls for separate motor enables--probably has to do with real XT compatibility.

                    I'm also correct in that you want link LK8 removed. So, a flat cable--you can use the current one with a 5.25 to 3.5 floppy adapter (used to be part of the mounting kit for mounting 3.5" drives in 5.25" bays):



                    Or crimp a 34-conductor IDC connector onto your present cable (take care to identify where pin 1 lies). No desoldering necessary.

                    Set the "A" drive to the first drive select (usually DS0) and the "B" drive to the second drive select (usually DS1).

                    You should be fine--just take care to remove LK8.
                    Reach me: vcfblackhole _at_ protonmail dot com.

                    Comment


                      #11
                      I may be misreading his original post, but I think he wants to put two floppy drives in his Packard Bell (Pentium), not his Amstrad PC 1512.

                      Comment


                        #12
                        Originally posted by Plasma View Post
                        I may be misreading his original post, but I think he wants to put two floppy drives in his Packard Bell (Pentium), not his Amstrad PC 1512.
                        You're right.

                        This is what happens when you get old; easily confused. And forgetful too. I have just remembered that there is a post over on the Vintage Computer Forums that I need to reply to.

                        Comment


                          #13
                          I missed that too--and I'm no spring chicken either. Topic drift. In my defense, the OP did start out by talking about his PC512.

                          The PB thing should be straightforward--if the PB is capable of supporting two drives. Some cost-reduced machines were equipped with support for only one drive.

                          If that's the case, you'll have to resort to something such as a Microsolutions Backpack floppy drive--or find an ISA controller card that has 2-drive support.
                          Reach me: vcfblackhole _at_ protonmail dot com.

                          Comment


                            #14
                            There is one more thing to consider here. Since you are using a QumeTrak 142, you will have an issue with pin 34 on the cable. The 3.5 inch drive uses pin 34 for DISK CHANGED. The QumeTrak 142 use pin 34 for READY. My solution was to modify the cable so that pin 34 is not connected at the QumeTrak but is connected on the other connectors. The following is a reply from Modem7 in another thread that might clear things up.

                            "In the early days of the 5.25" floppy interface standard, pin 34 was optionally used for a READY signal (floppy drive is ready). Some 360K drives generate it and some do not, and some (like the JU-455-7) have a jumper to select the desired behaviour.
                            The IBM 5150 and 5155 and 5160, as supplied by IBM, do not care what is on pin 34. If you look at the IBM floppy controller supplied in the 5150/5155/5160, pin 34 is not connected. Accordingly, the floppy portion of the motherboard BIOS doesn't care.

                            With the introduction of the IBM 5170, pin 34 is used by the supplied floppy controller, and 1.2M drives are required to supply a DISK CHANGED signal on pin 34.
                            The rules for the IBM 5170 are:
                            * 1.2M drive: Must generate a DISK CHANGED signal on pin 34. The controller and motherboard BIOS expects that signal from 1.2M drives.
                            * 360K drive: Generate no signal on pin 34, not even a READY signal. Disconnect pin 34.

                            Like the 5170's floppy controller, the XT-FDC controller has pin 34 connected. The 5170 rules probably apply. I'm guessing that your Qume 360K drives generate a READY signal on pin 34, and that was confusing the XT-FDC, until you disconnected pin 34."
                            Last edited by ibmapc; November 15, 2015, 09:41 PM.

                            Comment


                              #15
                              Funny, since the 142 uses an edge connector, I just put a bit of Scotch tape over the finger.

                              In reality, however, any BIOS that allows for configuration of a 360K drive will know to ignore the READY pin. It has ever been thus.
                              Reach me: vcfblackhole _at_ protonmail dot com.

                              Comment

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