Project: Switch for entering builtin monitor program.
Target : CBM 2/3/4/8000 series (read note!)
Time : 5 min.
Cost : ~ 3 US$
Use : start monitor from within an arbitrary program
Push-button switch between pin 1 (GND) and pin 5 (DIAG) of the
Note: This switch is said to work on PETs in general,
I only tested it on my 8296D, though. So to be absolutely safe that you don't
damage your computer in case you don't have the pinouts of the user port
for your specific model, attach the switch via a 470 Ohm resistor!
- G xxxx
- Go. Executes a program starting at xxxx.
- L "filename",dev
- Loads 'filename' from device number 'dev'.
- Displays memory contents: M start_address end_address
- Displays processor registers.
- S "filename",dev,start_address,end_address
- Saves memory from start_address to end_address to 'filename' on
device number 'dev'.
- Exit TinyMon.
- Modify memory (in output of 'M' command)
- Modify processor registers (in output of 'R' command)
- 1 single-pole push-button switch (normally open)
- 1 user port connector (edge connector, female)
- Solder push-button switch to pin 1 and pin 5 of the edge connector. Be
sure to not shortcut anything, insulate the wires between the connector
pins and the switch. I recommend using hot glue to both insulate and fix
- Now test the switch:
- Plug the user port connector into the user port
- Press and hold(!) the diagnostic switch
- While still pressing the button, switch the machine on
The machine should boot up without the characteristic beep
sequence and immediately enter the builtin monitor.
- If everything seems fine, you successfully made your own ultra-complex
diagnostic switch :-) Note that instead switching the machine on while
pressing the diag switch, you can also press the reset button instead
(while pressing the diag switch!).
- Are you sure that the push-button switch is normally OPEN?
Updated: February 18th, 1998
Created: January 28th, 1998
Status : Verified on January 18th, 1998
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!