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XT-FDC project level of interest

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    Thanks Chuck! That's helpful and hopefully we are close to figuring this out.

    For anyone else who would like to have a try at the build and test phase there is still one prototype PCB packaged and ready to go. Please contact me if interested. This would be for someone experienced with electronics project build and test and debugging circuitry. There is no point it of the PCB sitting on my shelf when someone could be hammering out the design.

    Thanks and have a nice day!

    Andrew Lynch

    Comment


      Andrew, check your layout VS your schematic please.

      Comment


        Originally posted by Crypticalcode0 View Post
        Andrew, check your layout VS your schematic please.
        Hi
        I have been double checking the schematic against the PCB layout. Am I missing something in particular?

        Thanks for the help. Have a nice day!

        Andrew Lynch

        Comment


          As I said, I have all the needed parts around to build a test PCB based on 82077AA-1 controller.
          My videos:
          IBM PS/1 model 2011 restored and enhanced
          IBM PC Advanced Diagnostics Cassette load

          Comment


            Found it--when I ran through all of the port addresses 100-7fff, a pulse appeared on /CS. So what address? I just hooked /CS to /IO CH CHECK (A1) and dropped in a handy TSR to dump the registers when it hit.

            Answer (I should have caught it from the schematic): The sense of A3 is wrong in the address decoder. You want to look for addresses on 3X0-3X7. Instead, the decoder is set up to hit on 3X8-3XF. I'll cut and jumper pin 16 of U6 to ground and continue my testing...
            Reach me: vcfblackhole _at_ protonmail dot com.

            Comment


              Thanks! That's great news!

              Sorry for the error. I stared at that decoder many times and that just slipped through.

              Very good news though. Please let me know how the rest of build and test goes.

              Thanks and have a nice day!

              Andrew Lynch

              Comment


                Okay, for those of you with the prototype board, don't bother to try and cut and jumper traces on U6 pin 16--there are +5 traces both on the top and bottom sides of the PCB that will make life miserable for you. The simplest thing is to clip pin 16 on the 688 short and just solder a wire between the pin 16 stub and pin 17.

                That being done, I've formatted, read and written 1.44M, 360K and 720K floppies both on primary 3Fx and secondary 37x port addresses. Only units 0 and 1 so far--I haven't tried the external connector yet, but I've got external drive boxes that should handle them.

                __________________________________________________ _____________________________________

                I've been doing some thinking. Given the semi-unobtainium status of the 8477/82077, would it be wise to buffer at least the external drive interface? I get a little nervous around external devices and if I were to make some magic smoke, I'd rather it be with some commodity logic parts instead of some hard-to-get part.
                Reach me: vcfblackhole _at_ protonmail dot com.

                Comment


                  Great work Chuck - as always!

                  Comment


                    Yes, good work.
                    I've checked my mail, and the XT-FDC card was there. Just now awaiting on some ordered parts.

                    Comment


                      Originally posted by Chuck(G) View Post
                      I've been doing some thinking. Given the semi-unobtainium status of the 8477/82077, would it be wise to buffer at least the external drive interface? I get a little nervous around external devices and if I were to make some magic smoke, I'd rather it be with some commodity logic parts instead of some hard-to-get part.
                      Hi Chuck! Thanks! What's the best way to do that? I am thinking three 74LS07s.

                      Also, have we given up on the DP8473? I'd like to at least give it a try. The main advantage is it supports some unusual modes but is also a hedge against parts obsolescence. Unfortunately, not a great one since it is probably more rare than the PC8477B. Are there any other options?

                      I am feeling good about the prototype board. The community investment in these four PCBs is paying off big time.

                      Thanks and have a nice day!

                      Andrew Lynch

                      Comment


                        Originally posted by lynchaj View Post
                        Also, have we given up on the DP8473? I'd like to at least give it a try. The main advantage is it supports some unusual modes but is also a hedge against parts obsolescence. Unfortunately, not a great one since it is probably more rare than the PC8477B.
                        The parts list quotes "DP8473V". Out on the Internet is both DP8473V and DP8473AV, with the DP8473AV appearing (on the surface) to be readily available. I have looked but have yet to establish the difference between the V and AV versions (i.e. if the AV is a substitute for the V version).

                        Comment


                          Originally posted by modem7 View Post
                          The parts list quotes "DP8473V". Out on the Internet is both DP8473V and DP8473AV, with the DP8473AV appearing (on the surface) to be readily available. I have looked but have yet to establish the difference between the V and AV versions (i.e. if the AV is a substitute for the V version).
                          Hi
                          I don't have a datasheet but will check it out later today. Do the pinouts match? If they do its probably worth a try at least. Some issues like this can really only be settled by trying it in build and test. If it is simply dead or severely brain damaged then so be it and we can drop it. However if it can be made to work we should at least consider it.

                          Thanks and have a nice day!

                          Andrew Lynch

                          Comment


                            Originally posted by lynchaj View Post
                            Hi Chuck! Thanks! What's the best way to do that? I am thinking three 74LS07s.

                            Also, have we given up on the DP8473? I'd like to at least give it a try. The main advantage is it supports some unusual modes but is also a hedge against parts obsolescence. Unfortunately, not a great one since it is probably more rare than the PC8477B. Are there any other options?

                            I am feeling good about the prototype board. The community investment in these four PCBs is paying off big time.h
                            7407s will work just fine--or you could assert /INVERT and use 7406s, but then you'd have to invert the input signals as well (74LS14?).

                            The DP8473 is a great controller, but it's very scarce and, AFAIK, there are no pin-compatible substitutes. Future Domain, Ultrastor and Adaptec (and probably DTC) used them at some point, but I don't know if they ever made it onto many motherboards, which might account for their scarcity. Oddly, the DIP (2 drive) version is more common than the PLCC. About the only novel use is in writing 128-byte MFM sectored data. I have more fingers on one hand than the number of formats that I've seen that way.

                            At least that's my take.
                            Reach me: vcfblackhole _at_ protonmail dot com.

                            Comment


                              Andrew, could you adjust your copper pour or traces routing so there are no ground fingers between signal lines?
                              These are bad at higher frequency because they act as antenna.
                              Currently checking signal lines if they are centered on the Via's without any offset, this is something that is known to cause problems too.

                              Comment


                                Originally posted by Crypticalcode0 View Post
                                Andrew, could you adjust your copper pour or traces routing so there are no ground fingers between signal lines?
                                These are bad at higher frequency because they act as antenna.
                                Currently checking signal lines if they are centered on the Via's without any offset, this is something that is known to cause problems too.
                                I have to admit that I was a bit surprised by the routing on the PCB. In particular, note that the +5 first point of connection after it leaves the bus is a signal pin. I guess the auto-router doesn't treat power buses specially. If I were doing a hand tape-up of a board (does anyone do this any more?), I'd do the power rails first, then work the signal lines around them.

                                But I'm old and not up to speed on "modern" stuff.
                                Reach me: vcfblackhole _at_ protonmail dot com.

                                Comment

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