IEC reset

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Don't Panic. Please wash hands.
  • Hello,
    1st difference,that I noticed,when I migrated from my C64C to MK2 is,that when I do perform a C64 reset (via power switch or via cart), it does also reset the IEC.However there is no option in the setup for this.Does the board design allow to have a option for this in the future fw release? I can't dig in the drive mem when I needed to in current state :(

  • Uhm, the reset pin on IEC is supposed to work like this. It also does the same with a correctly installed (*) reset button on that C64C :)


    That said, i dont think it can be changed in a firmware update.


    *) That means its connected internally to the reset circuit, and not misusing an output (!) pin on one of the ports. That will result in the behaviour you describe on some (!) C64 boards.

  • Does the board design allow to have a option for this in the future fw release?

    Firmware cannot change the behaviour of a hardwired circuit.


    The first C64 baords had the reset line of the IEC wired directly to the IEC circuit of the C64. This made reset-buttons on the IEC port possible. However, with many devices connected to the IEC at the same time (up to four floppies, a printer and a plotter), the reset line was pulled up my each of these devices and the computer's internal reset circuit had trouble dealing with the load.


    Starting with the second revision of the C64 main board, Commodore introduced an open-collector driver "from computer to IEC" which was strong enough to deal with a higher number of external devices.


    No Commodore computer has ever had an open reset line on the IEC port. What you are asking for is something that was hacked by crackers back in the day - you may have forgotten about it after all these years :-)


    The C64 Reloaded MK2 of course also implements "open collector driver on IEC", and if you want to apply the hack of "reset C64 but not IEC devices", you'll have to remove resistor R80, which is the base current-limiting resistor for transistor Q13 that pulls low on the IEC-reset line.

  • That's a bit strange, the C64C, was not modified for no IEC reset , still has the factory seal unbroken,so that's why I was not aware about this behaviour,.Long time ago I had to equip my drive with it's standalone reset button.The C64C does IEC is reset, but only during power up.
    I thought,that during the MK2 design,that selectable IEC reset was taken into account,that's why I asked about the firmware change.

  • Hi all, then from my experience I verified that the C64 up to the assy 250407 the reset was unique, and active to the serial port. From the assy 250425 onwards, the reset is no longer connected to the pin of the serial port, but only by the user port and the cartrige port. By default the assy 250425, assy 250466 and assy 250469 the reset is not connected to the serial port, however studying the layouts of the boards, one can find the points to be joined to make the reset of the serial port active, but doing so also resets devices connected to it.