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I can't make John's serial board with His Z-80 Board

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    Hi All;

    Thank You, Don for the offer, fortunately I got my Programmer to work, on my newly Installed XP system..

    So, that is a step in the right Direction for me.. I am going to go to John's site and download the file for the Z-80, and see if I can make any progress..

    Something to do tonight..

    THANK YOU Marty



      Here is my first attempt.

      I can't guarantee anything at all though ...

      You should be able to import the source file (Monitor1.txt) into to be able to modify it yourself and regenerate a new HEX file.

      My apologies to John in advance for the horrible hacks...

      Attached Files



        I forgot to mention that the serial port is initialised to 38.4 kbps by default to save you a bit of time finding it out for yourself.



          Hi Dave;

          Thank You, I didn't know, so I can try this later, I had already tried 19.2K..

          THANK YOU Marty


            You will also require the hardware handshake lines cross-connecting don’t forget. RTS to CTS should be enough to get data out of the SCC. Set your receiver to 8 data bits, 1 stop bit and no parity to start with.

            If you don’t see any characters on your terminal/emulator, have a look at the chip select line of the SCC when you reset the CPU card and check for a burst of activity with a logic probe, scope or logic analyser.



              Hi All;

              Thank You Dave for the added Information..

              I tried Your files yesterday evening, and they didn't work, also the Rom Select Led on the Z-80 didn't come on as with the regular full eproms..

              I also need to take a closer look at the file on the eprom, and see (1) how much of the eprom space is used, and (2) if possible see where you had as a starting address, whether it is/was E000 or F000 or something else.. The regular Eprom is set for F000..

              I have to take a look at a few things first, before making any further assumptions.. I went to bed last night all confused, as every time I tried to ohm out what pins went to what pins, I got different results.. So, I know I was too tired and had to just get away from it..

              I could be Wrong, but some of the connections (pin wise) on the two jumper blocks (P60 and P62) don't match the schematic, between the serial connection and the Max232 connection, which is where I am having the most trouble at the present..

              THANK YOU Marty



                Yes, a good nights sleep is often good!

                The monitor code resides at F000h. This is the entry point.

                What type of EPROM are you using?

                I did read somewhere about having to program the code into the upper part of the EPROM (i.e. you need to add an offset to the HEX file when loading it into the EPROM programmer if the EPROM is larger than $F000 to $FFFF (4K)).

                This may account for your problems (at least in part)?



                  Hi All;

                  Dave Thank You for Your prompt response..

                  The Eprom I have is a 28C64..

                  THANK YOU Marty


                    >>> Dave Thank You for Your prompt response.

                    No problem.

                    a 64kbit device = 64*1024/8 = 8K Bytes. This is twice as big as the monitor code.

                    My guess would be (if you put the EPROM back into your programmer) that the monitor code has been blown into the first 4K of the EPROM rather than the last 4K of the EPROM.

                    The relevant text on the S100 Computers website for the Z80 card is:

                    Note if you decide to use a EEPROM such as a Samsung MK28C64A 8KX8, you have to place it at an 8 K boundary. So in high RAM this would be at E000H.  If you want to use E000H-FFFFH for your monitor then that's fine. More typically however you will need only 4K for a monitor starting at say F000H to FFFFH.  In this situation you can either program the second 4K of the EEPROM's 8K space and  jumper JP8 1-2  and P39 5-6 (i.e. utilize A1 and A12) and set the POJ jumper P3, to F000H, or alternatively just program the lower 4K of the EEPROM's 8K space and force the EEPROMS A12 line to low, so jumper JP8 10-2 as before, but jumper P39  3-4.   BTW, you can have a second completely different second monitor in the EEPROM switchable to the upper or lower half of the EEPROM with jumpers P39 3-4 or 1-2.  
                    You must also be sure to "burn" your monitor into the upper or lower half of the EEPROM. (For the upper half, using a Wellon VP-280 Programmer, the "Load Buffer Address" would be 1000H, the "File Address" is F000H).
                    It seems as though there are lots of options, it depends upon what links you have configured as to how you must program your EPROM...

                    I am going out for a walk now - but will be back shortly.



                      Hi All;

                      Dave, Thank You for Your Response..
                      I do not have the same programmer as John's programmer.. And, so I have not been able to figure out "HOW" to lengthen and copy the code to the upper half..
                      I have imported Hexedit and hex2bin, to try and help, but, so far I cannot get hex2bin to convert my Hex file from the eprom programmer to a binary file, that I can then edit with hexedit..
                      My other for now option is to use a 2732 Eprom, but, I don't know how to set the jumpers on the Z-80 card for this Eprom instead of a 2764 type of eprom, the Documentation isn't clear to me on how to do that..

                      Hi All;
                      I found the jumper for the 2732.. so I'LL try that.. I will let You know how that goes..

                      THANK YOU Marty
                      Last edited by Marty; April 16, 2020, 07:15 AM.


                        Can I ask you exactly which revision of the Z80 CPU board you have?

                        There appears to be at least three different versions from what I am reading.



                          Hi All;

                          Dave, Thanks for asking, I have version 2 of the Z-80 Board, and version 3 of the Serial Board..

                          I have things back wired up (as near as I can tell) correctly to the serial port, that goes to the PC..

                          The Led at least indicate it is correct.. Now to try Your suggestion on scoping the SCC IC..

                          THANK YOU Marty


                            From the web page:-

                            "Serial IO Board Version V3.1
                            The demand for this board has been quite large. A third version of this board was laid out. This version is called V3.1. The first batch was made by PCBCart in Jan 2016. It is identical to the above V2 board except that a more detailed Silkscreen was drawn up. This one has labels over all the IC's, and better legends over the switches and connectors. The KiCAD and related files are presented below." Does not look like you are reading things carefully!

                            You must change the lookup table in the monitor if you want to change the baud rate as Dave points out. You can reassemble the monitor at a lower address and run it in RAM if you have the ability to load data into RAM.


                              Looking at V2 of the CPU board you have a couple of options:

                              Install a 2532/2732. This is a 24 pin device and you are putting it into a 28 pin socket. I don't like doing this myself as the possibility of inserting it into the wrong pins by mistake are extremely high...

                              Install a 2764. In this case:

                              JP8 needs to be installed on 1-2 (Address line A11 to the EPROM).
                              JP9 needs to be removed (No Connect to pin 26). I see on the web page that JP9 needs to be installed for a 28C64.
                              JP10 needs to be installed to enable the on-board ROM. I don't see any mention of this jumper on the web page?

                              P39 needs to be linked correctly...

                              For the full 16K EPROM to appear in the memory map you need to install 5-6. This assumes that you program the monitor into the upper half of the EPROM.

                              If, however, you link P39 3-4 instead, this causes address line A12 of the EPROM to be permanently connected to 0V and only the first half of the EPROM can ever be addressed.

                              I still need to look up the other links to see how the restart vector is accomplished for F000h. EDIT: P3 removed sets the boot address to F000h.

                              Can you tell me what links you have installed and removed please and I will try and find out if that is a valid configuration.

                              Last edited by daver2; April 16, 2020, 10:01 AM.


                                Hi All;

                                Thank You John and Dave for Responding..
                                John, what am I not reading correctly, You state that version 3 of the serial board is schematically the same as version 2 of the serial Board.. I don't see what that has to do with the issue I am dealing with at the Present, I have the Schematics here on my Computer and I use them to ohm out how to wire up P60 and P62 and it looks like I have it correct, as the four Leds are on for CTS, RTS, DTR and DCD..
                                So, what I need from You (John) is Do I have the Correct baud rate for the serial board, I have it at 38400, Yes, earlier I had it at a lower rate 110 to follow the signals thru the various IC's..
                                Dave, And for now I have to use 2732's Eproms, as I cannot put the program into the second half of the 2764's, So, (John) what jumpers on the Z-80 do I need to make it work correctly, especially P38, I know about JP9, do I need to change anything else ??

                                At present I don't have the ability to upload from the PC to the serial board, I am awaiting the USB to parallel IC..

                                THANK YOU Marty