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  • #9588
    Just4Fun
    Participant

    After playing around with a Z80 and V20 CPU, a 68000 CPU could not be missing… 🙂
    After reading some documentation I started a new one “travel” choosing the version with physical bus a 8 bit (68008) to simplify the HW as much as possible.

    Since the 68008 it exists only in HMOS version and not CMOS, I had to necessarily change the MCU which will emulate all the various I / O chips around it. Compared to previous versions of SBC cards (Single Board Computer) with Z80 and V20 CPUs (Z80-MBC2 e V20-MBC) both in CMOS version, I had to look for an MCU that had TTL compatible GPIOs, which the Atmega MCUs I had previously used do not guarantee (see the related datasheets).
    Another requirement was the DIL package and obviously the low cost. So in the end the choice fell on the PIC18F47Q10 (red custom photo card):

    For now I am preparing a breadboard to carry out the first tests. We'll see what comes out of it…

    #9591
    Picmicro675
    Moderator

    Congratulations on your work.
    I make a note about breadboard tests. Just to name one, I cannot swing the quartz a 20 MHz of a pic15F675. It's already the second MCU I've tried and nothing.
    It amazes me that in some cases it doesn't get anywhere. Despite my articles being mostly on breadboad, but I would really like to understand if there is a way to test the quartz and perhaps with an external oscillator check if the MCU takes the clock.

    #9593
    Just4Fun
    Participant

    No wonder a quartz oscillator doesn't work on breadboard at all… there are too many capacitances and parasitic inductances, and disorders in general…
    I also have had problems with some MCUs… in the end to solve I used the internal oscillator e, if necessary, an EXO-3 programmable external oscillator:

    E’ a little bit a lottery the quartz on BB (breadboard).

    Maybe as a last resort try removing the load capacitors (load capacitors) and to connect only the quartz.

    If you have to do some tests, you should use a PCB “veroboard” O, better, a test PCB like this (note the quartz socket made with the pin headers):

    It is not clear to me what you mean by “check if the MCU takes the clock”, but if you want to use an external clock you can use an oscillator “integrated” come l’EXO-3 (if you can find it) or any oscillator a 4 pin (those with a metallic case).

    • This reply was modified 9 months, 3 weeks ago by Just4Fun.
    • This reply was modified 9 months, 3 weeks ago by Just4Fun.
    • This reply was modified 9 months, 3 weeks ago by Just4Fun.
    • This reply was modified 9 months, 3 weeks ago by Just4Fun.
    • This reply was modified 9 months, 3 weeks ago by Just4Fun.
    • This reply was modified 9 months, 3 weeks ago by Just4Fun.
    • This reply was modified 9 months, 3 weeks ago by Just4Fun.
    #9606
    Picmicro675
    Moderator

    As you say it is a gamble to make the quartz work, To remedy a bit, I prepared a small base with the quartz and the two capacitors mounted.
    quartz
    About this i take the clock, I would mean the way to create an external oscillator and put it at the clock-in of the MCU.

    #9608
    Just4Fun
    Participant

    I don't think this improves the situation because you put them in the BB anyway. What I suggest is to make a PCB with the MCU and the oscillator. Then you can use pin headers to insert the PCB onto the BB as if it were a breakout board.

    #9610
    Picmicro675
    Moderator

    You are very right.
    This is a gimmick that assures me (badly) that the contact is well made since the leads of the 3 components are less than half a millimeter and secure contact was not achieved.
    Agree that it takes a small board, as you showed it above, to have the most guaranteed swing. I would say that I will make an assembly on millefori that contains the quartz welded and in close contact of the MCU

    #9617
    Just4Fun
    Participant

    After a while of “flapping” eventually the CPU 68008 on breadboard gave a tangible sign of correct operation.
    This is the classic test “Hello world” written in 68k assembler:

    and this is the current one “situation” of the breadboard:

    Now the next step is to run a Basic interpreter for 68000…

    #9619
    Picmicro675
    Moderator

    Of course that 68K in the jungle of those connections must be well fixed. For the clock you use the EXO-3, vero? Basic, that of Sinclair's Quantum Leap ?
    Maybe you could even resurrect a Zyxel analog modem, which I almost paid 2 millions of lire (how to say almost 2 months of salary).
    I admire a lot your great invective for these projects.

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