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

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    Frank: is your model 4 a 128k ram version?

    I found the original source before it was hacked for "IDE". Much easier to work on the original which really doesn't need that much change. I DO see the format routine writing to the middle of each sector. At the moment its writing the wrong stuff I think. It looks like the format routine builds up this GAT buffer and tries to write that to the directory track. I will look at it today.



      128k Gate Array Model IV. The newer style with green screen etc. As seen here in a comparison of the 2.
      Last edited by Chromedome45; June 20, 2013, 11:37 AM.


        I am sending you an image file in email to verify your setup.



          Some positive news to report. Matt sent me a CP/M test program that formats and verifies a CF Card and it worked fine. Now have an M: drive and can copy files to the CF card. So Pearce: looks like this is a working design in so far as CP/M goes. Matt is still hacking away at the LDOS drivers.


            I've finished off the PCB design - a few small changes:
            • Added buffering to the remaining four unbuffered lines via another 74ACT32
            • Replaced 2-pin header for power with screw-terminals

            If we're generally happy I'll send the design to fab.


              Will add ACT32 in AM.
              Last edited by Chromedome45; June 21, 2013, 07:44 PM.


                ACT32 added and appears to be working fine. CP/M formatted and verified the CF card. Pearce: I guess you can finalize and have boards made.

                As far as working in LDOS the driver is being worked on.

                Oh how much do you estimate a board will cost? Most likely I will take one.

                Some pics of the prototype. Notice that the even numbered pins on the 50 pin connector are towards the inside. Because of the way my TRS-80 cable was made this is the way I had to do it. Well it was easier for me to do it this way. also the bottom could looked neater but with additions of wires etc. it's just the way it turned out. But it does work so not to big of a deal.

                and the prototype in action using CP/M Pics
                Attached Files
                Last edited by Chromedome45; June 22, 2013, 04:15 AM.


                  Way to go, Frank!! You've even got it laid out on a RadioShack protoboard. Impressive!

                  I'll certainly be interested in a couple of these boards when available. My Mod 4 has been sitting in the garage for a few years. This will be a good excuse to bring it in and fire it up.


                    Originally posted by Chromedome45 View Post
                    ACT32 added and appears to be working fine.
                    Good news! And some very nice work on the prototyping there

                    Originally posted by Chromedome45 View Post
                    How much do you estimate a board will cost?
                    Bare PCBs will be GBP 10, including shipping.

                    Originally posted by Chromedome45 View Post
                    Notice that the even numbered pins on the 50 pin connector are towards the inside.
                    Do we need to change the pin header on the PCB?


                      Getting a little further with the LDOS drivers. There is some kind of Directory size issue I need to sort out but formatting is definitely working. Its the initialization part that is messing up.



                        Pearce: As I said it may be just my cable. But compared to the one TRS-IAN is using it looks identical see pic in my next post. I used an old SCSI cable and added a 50 pin card edge connector to it. So I would leave it alone. Mainly because my IDC connector end is upside down when connected! See pic in my next post as well and you will see the connector is definitely upside down. But this is how it works for me on this prototype

                        But this is what I have found out. The even number pins are facing the out side of the bus connector and the odd pin are towards the inside of the connector. Worst case scenario would be just to flip the 50 pin connector around 180 degrees.

                        To simplify things here is a picture showing the Even pins RED "E" and the odd pins RED "O" Also a red line to indicate pin 1 end. So hopefully no confusion.
                        Attached Files
                        Last edited by Chromedome45; June 22, 2013, 10:45 AM.


                          How are you connecting this to a TRS-80 Model 4? I must have missed something, but I can't find in the thread how the board connects to the TRS-80. You mention a 50 pin card edge connector, but i thought these only had an RS-232 and a parallel port.


                            Hey Chuck, nope they have a Floppy port 34 pins RS-232 25 pins Printer port also 34 pins and the expansion port which is 50 pins. This is the Cable TRS-IAN sells with the FreHD HD emulator (PIC). The 50 pin IDC hooks up to the Cheapo IDE or the FreHD. I have attached a couple of picture to explain. The 2 picture is with the Cheapo hooked up to the expansion port. The 3rd Picture shows the port connectors. From the top down is: 34 pin floppy port 25 pin RS-232 facing outward because mine is a Gate Array model IV. 50 pin Expansion for the cheapo or the FreHD or a real TRS-80 hard drive and last is the 34 pin printer port.

                            So hopefully this clears it up some.
                            Attached Files
                            Last edited by Chromedome45; June 22, 2013, 10:40 AM.


                              Here are the pictures for the model 4P I have.

                              For orientation Pin 1 is on the right in both pictures. The ground lines are on the bottom of the connector and the signal lines are on the top. That puts even on the bottom and odd on the top.




                                Yes I can actually see the number 50 in the 1st pic. The info about the Modem is that at the bottom portion of the 4P? And the FCC warning about interference is at the top? If so it means even is on top! Pin 50 is a dead giveaway. It is on the even side 2-50 and would put pin 1 on the right side same as mine. If you are doubtful take an Ohm meter check touch pin 50 on the left end and then touch any pin on that row. Should show a short. That's how I did it with mine.
                                Last edited by Chromedome45; June 22, 2013, 10:55 AM.