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Format with write protect on...

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    #16
    The FDC should abort the format operation, which is what I find puzzling.

    Comment


      #17
      The BIOS format track operation does not verify that it actually wrote anything. The formatter follows up with a read/verify track operation, but usually only checks that sectors are readable, not the content. A formatter may check to see if things are written properly when it writes file system information.

      All of those would return an error upfront if a write protect is detected. So it sounds like a write protect signal is just not getting to the motherboard.

      So verify that the drive is generating a write protect signal, and verify that the cable is good.

      Comment


        #18
        Check(G) - I agree. My theory so far is that the FDC IC just doesn't write to the disk with a format command, but yet doesn't report an error either.

        SomeGuy - Originally the write protect always indicated disabled, irregardless of whether the WP is on or off. The optical sensor was bad. I replaced it with an OPL530. Now it works as expected when doing everything but formatting. If I try to write to a write protected disk by copying or deleting a file, it will fail properly with a write protect error. The format however works differently, it will go through the motions of formatting, but does not actually change the disk sector contents. It then only fails at the end when it tries to write the directory. You can still read and run the files.

        Comment


          #19
          That the FDC itself responds to commands would lead me to check the interface (buffers and receivers) ICs first after verifying the cable connection.

          A failed 765 FDC is not unheard of, but usually if they fail, they simply flat out fail.

          Comment


            #20
            I've got that bad 7417 that I need to replace - why would it see the write protect when copying a file, but not when formatting a track?

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              #21
              It could be the software that does the format. The FDC controller sees it but the software could be ignoring it until it did the first data write. Also, do remember, the response is for software to do something about. If the software just continued to the the format track and ignore the write protect status, it would look the same as the controller not seeing the write protect. Do remember the controller doesn't treat the format of a track the same as a write. it is a separate special operation of the controller.
              Dwight

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                #22
                But the format will abort and throw an error status that's hard to ignore.

                Try starting a format and removing the floppy mid-way. If the format continues, that should tell you that the software (more likely the disk driver, as under DOS 3.3+ format is performed by the program calling an IOCTL function) is really stupid.

                Comment


                  #23
                  Dwight - I think the fact that it is treated differently (format vs. write) is maybe why it is happening. If I use the same format command on another system, it fails immediately when the write protect is set. My theory is that this particular FDC accepts a format command and doesn't respond with an error condition while other FDC's do.

                  Comment


                    #24
                    Your FDC is a licensed clone of the NEC D765. I doubt that they did anything original.

                    Comment


                      #25
                      I think I have a NEC D765 in my chip collection, I could swap it out and see if it behaves differently.

                      Once I get the drive running again (I've got to fix a 7417 IC), then I can try some of these tests and maybe we can figure it out for good.

                      Comment


                        #26
                        Thank you--I think that we've beat this one to death for now.

                        Comment


                          #27
                          Bad 7417 replaced with a socket and a new 7407. This fixed the motor drive, so the 360K drive works again. I connected up the GoTek as well, and they both work fine together again (before drive B: was staying light on at bootup). The motor runs irregardless of which drive I am accessing (360K or GoTek).

                          I tried to format a disk with write protect again and it still does not fail at the beginning, but goes through the motions of the format. Maybe a bit slower than a real format. I imaged the disk ahead of time, tried the write protected format, then imaged it again. Both images are the same proving it does not change any data on the disk. It still fails at the end of the format.

                          My controller IC is in a socket so i can easily try changing it, it says:
                          R6765P
                          15601-16
                          8445

                          I have these 3 IC's I could try - I don't know which might be compatible or not:

                          NEC D765AC-2 8733KV NEC USA
                          WD37C65C-PL 00-02 9122 E 2509824-3505
                          WD37C65-PL 00-02 8745 051119101

                          Comment


                            #28
                            Datasheet says that it's a NEC D765.

                            The WD37C65 is a very different chip that contains the "all in one" logic for the PC.

                            Comment


                              #29
                              Okay; I'll try the NEC and see if it acts differently. I somewhat remembered the WD not being the same.

                              Comment


                                #30
                                Same result with the NEC chip.

                                If write protect is confirmed to be working, is there any other signal that could cause this?

                                Could it be a BIOS issue? I know chris_nh tested it with a Tandy 1000 w/ 360k drives, but I'm not sure which Tandy 1000 that was.

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