Reset buttons and floppy drives

Schema · Post by **Schema** » Thu Jul 28, 2005 8:17 pm

I just discovered something really odd when testing my prototype cartridge on my real VIC - something I would never have found in an emulator

When a floppy drive is connected to the VIC and turned on...the reset button on the cartridge doesn't work. Turn off the drive, or disconnect the serial cable, and the reset button works again.

Plus, the reset button on the cartridge resets the drive if the VIC is powered off

That doesn't make any sense to me, any ideas?

I have a 100 ohm resistor in series with the reset button as per Ray Carlsen's suggestion, for safety...could that be causing a problem? Too much load for the reset line to get pulled to ground maybe? Though this works on a C64, and I didn't think the serial and computer reset lines were connected.

Boray · Post by **Boray** » Fri Jul 29, 2005 1:42 am

I have my reset button plugged into the free serial port of the diskdrive...

/Anders

carlsson · Post by **carlsson** » Fri Jul 29, 2005 5:46 am

There is also a reset pin on the user port, if you wish to compare how it works. Remember that the VIC resets or at least causes an initialization of the drive even when you power it off, unlike the 64 which only initializes the drive on power on. I don't know if that is part of the answer.

Schema · Post by **Schema** » Fri Jul 29, 2005 7:51 pm

carlsson wrote:Remember that the VIC resets or at least causes an initialization of the drive even when you power it off, unlike the 64 which only initializes the drive on power on. I don't know if that is part of the answer.

Mine doesn't do that, as far as I can tell.

Anyway, it seems the problem was the 100 ohm resistor. I removed it, and now the reset button works perfectly. It still works on the drives when the VIC is off, too.

tlr · Post by **tlr** » Sat Jul 30, 2005 2:06 am

Schema wrote:Anyway, it seems the problem was the 100 ohm resistor. I removed it, and now the reset button works perfectly. It still works on the drives when the VIC is off, too.

This resistor would form a voltage divider with the total amount of pull-up on the reset line. (both the drive and the vic20) If the pull-up was equivalent to, say 1k you will get a 1/11 voltage division. If the pull-up is connected to 5V, which it is, the voltage of the reset line will then be ~450mV, which may, or may not, be to high to be detected as a valid 0 for certain chips.