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Cheapo IDE interface for Model 4p running MM CP/M

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    The FreHD emulates a real TRS80 hard drive, so you don't need to use custom drivers. It uses a FAT on the SD-card, and the image of the hard drive is compatible with the TRS80 emulators, so you can prepare/fill your hard drive image on your Mac/PC and use it directly on the real TRS80. You can also have multiple hard drive images on the same card, backup of your hard drive is easy, etc... The price is that you need more hardware (GAL/PIC), but you have more flexibility...

    On the price side, a GAL and a PIC are cheap, but you need a PCB, etc... The design is open sourced, so enthusiasts can rebuild it. (At least one guy recreated it on a breadboard...)


      Oh yeah better way to go. But I like building things from scratch and see if it works. If not than I will definitely get a FreHD!


        "So to recap all Address lines and most of the control lines are being pulled up through a 1k resistor to VCC except /EXTIOSEL. Line correct?
        just really want to be sure."

        Yes, you have it correct. I added a 220 ohm pull-down resistor to the EXTIOSEL to help with the biasing.



          Hey matt, Ok got it built and am not getting the correct response when check Hex port 40. According to the original schematic documentation. Says when checking the port should get a response of 80 or 88 I get 8. What do you get. (it's run from disk basic under TRS-DOS 6)

          All address lines except A3 are pulled up. A3 is not connected. Should I pull up anyway? All control lines are pulled up except the aforementioned /extiosel. So you say use a 220 ohm and pull it down? Also does reset line get pulled up?

          Do me a favor. Of these control lines which get pulled up? This is on the TRS-80 50 pin side.

          /in /out /reset /iorq

          on the 40 pin ide side /iow /ior /cs0

          And last but not least the LS85. Verify pins 14,3 get pulled up and 9,11,1,2,4 are at ground. Sorry a lot of questions.


            Hopefully I get all these question right and win the Twinkie.

            1) You should get 80 with disk basic under TRS-DOS 6.

            2) I have all the address lines pulled up but I guess you could leave A3 as is.

            3) I added a 220 ohm pull down to the extiosel line to help with the biasing.

            4) I added 1k pull-ups to: /in, /out, /reset and /iorq on the TRS-80 side.

            5) LS85: 14 and 3 are pulled up. 9,11,1,2 and 4 are at ground.

            If you have turbo pascal I can send over my test program. Might be a lot easier than basic if you know pascal. + its has the CP/M format routine.


              First cut of PCB - needs a bit of work on the routing still.

              Image and schematic here.


                Need to also add a 220uF cap low esr to the +5 volt line as well. Assuming you are going to use an onboard regulator like a 7805.


                  Matt, Noticed my 50 pin card edge is messed up specifically pins 1,3,5,7,9 and of course these are the address lines!


                    oops. accidents happen.

                    PCB looks good. pin 14 and 3 of the LS85 should be pulled high though a 1k resistor. I probably missed something but it doesn't look like the a0-a2 are connected on the schematic. If you add an LED with a resistor to Vcc you can connect the other end to DASP- line (39) on the IDE interface for an activity lite.

                    Scary how fast all this can be done..



                      Matt, The value of 80 on port 40 is that with a drive connected or none?


                        Thanks, I added a solder-side image to the archive, which has the address lines on it.

                        I've not used pull-up resistors on 74LS inputs before? Good idea on the activity LED, I'll add that on.


                          Input from port 47h should give 80 decimal with drive connected.



                            On port H47 I am getting 80 but when I try to load the driver it hangs. Port H40 give me 0 I thought that ports 40-47 should all be 47?


                              There are actually a bunch of ports. For ide non lba mode it's like this:

                              Port, reading, writing (base 40h)

                              40,Rd data,Wr data
                              42,sector count, sector count
                              43,sector number, sector number
                              44,cyl low, cyl low
                              45,cyl high, cyl high
                              46,select head/drive, select head/drive
                              47,status, command



                                Yeah guess I need to debug the board then.