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Serial Bus Reset Switch

Project: Switch for resetting the serial bus
Target : C64
Time   : 15 min.
Cost   : ~1 US$
Use    : Revive hung up floppy drive without switching the drive
         or the C-64 on/off.


Switch between pin 2 (GND) and pin 6 (/RESET) of serial bus jack.


Switch which shortcuts pin 2 (GND) and pin 6 (/RESET) of the serial bus jack in the C-64. This causes the drive's CPU to excecute the drive's ROM reset routine.

Note: It is not a good idea to use a serial bus reset switch in old C-64s, because the serial bus reset line is directly connected to the C-64 system reset. This means resetting the serial bus results in resetting the C-64, too!
In newer C-64s (ASSY/PCB NO. greater than 250407) the serial bus reset line is usually decoupled from the system reset by a diode. On the smaller PCBs (found in C-64 II/c) you might find the serial reset line not at all connected to the system reset.
To find out whether your C-64 can be upgraded with a serial bus reset switch, shortcut pin 2 and pin 6 of the serial bus jack using a piece of wire. If your C-64 resets, you should not use the serial bus reset switch.

Note #2: There are two further variants of the serial bus reset switch: the first one is a reset switch built into a floppy drive (front panel) which is also useful if you want to quickly gain control over your PC-1541 transfer program again after an error; the second variant is a portable reset switch built into a DIN plug for the serial bus jack.



  1. Pull off all cables, then open case.
  2. Solder cable to switch.
  3. Solder one wire to pin 2, the other one to pin 6 of the serial bus jack from inside.
  4. Connect power plug, switch your C-64 and floppy drive on.
  5. Press the serial reset button. The drive's motor should be spinning and its LED should be lit. After a short delay, all activities should stop.
  6. If everything seems to be ok, attach the switch to the case and close it again.

Possible failures

Updated: January 7th, 1998
Created: January 29th, 1997
Status : Verified on September 23rd, 1997

Site copyright © 1997 by Marc-Jano Knopp
This document is part of MJK's Commodore 64 & LCD Page
Brought back to life by Peter Schepers, Dec 10, 2005 because I really liked this site!