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Adding reset button to C64

marc.hull

Experienced Member
Joined
May 26, 2007
Messages
107
I'd like to add a reset button to my C64 and assume it is as simple as grounding out the RST pin on the 6510 with a momentary contact switch and filter cap. My questions are

1) is this all there is to it ?

2) I have seen two pinouts for the 6510. One show PIN 40 to be RST (labeled 6510 CPU) and another 2 show PIN 1 to be RST (labeled 6510-1 and 6510-2)

Thank you...

Marc
 

Chuck(G)

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Jan 11, 2007
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Assuming we're looking at the schematics for the same rev board, a better place for a reset button would be between ground and pin 8 of U56 (the NE556 timer) at the junction of that pin, R50 and C105. The NE556 is used as a one-shot to generate a reset pulse when power comes up. Using a pushbutton there would make for a nice clean (without any bounce) reset.

(Disclaimer: I am not a C64 owner, nor do I want to become one)
 

jthiemann

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Dec 6, 2009
Messages
38
Location
Montreal, Quebec, Canada
I'd like to add a reset button to my C64 and assume it is as simple as grounding out the RST pin on the 6510 with a momentary contact switch and filter cap. My questions are

1) is this all there is to it ?

It's what I did "back in the days..." - it'll be good enough. Maybe put a small (1k or less) resistor in line, for safety.

2) I have seen two pinouts for the 6510. One show PIN 40 to be RST (labeled 6510 CPU) and another 2 show PIN 1 to be RST (labeled 6510-1 and 6510-2)

Thank you...

Marc

You can use the reset line on the user port, expansion port or even the serial port (didn't work on all models) - once one could buy DIN plugs with a button in it as a cheap removable reset button. That way you don't have to worry about the CPU pinout.
 

carlsson

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Yep, I agree with jthiemann. There are plenty of reset lines on the expansion ports if you want to avoid internal modifications. I suppose you could even trace where those lead and hook your button to the same lines. Note that putting a reset on the IEC/serial port will cause any floppy drive to reset as well. If I recall correctly, an user port reset button may work differently.
 

MrRobot

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Mar 24, 2010
Messages
9
Location
Finland
I'd like to add a reset button to my C64 and assume it is as simple as grounding out the RST pin on the 6510 with a momentary contact switch and filter cap.

Marc

As noted before, the best way to add a reset button is to use the reset lines on external connectors. I couldn't find a schematic of the C64 user port, so I took a quick peek at how I wired my reset button years ago (has always worked well, used it a lot when I did assembler). Looking from the back and top of the motherboard, I've soldered the switch to the first and third lines. There's an open gap between the first and second line. I've soldered them just before the edge where the connector starts, so that the user port can be used as normal (never used it).

All you need is a couple of wires and a button with a spring so you can short the lines. I remember this was the easiest and cheapest solution I found back when I needed a hard reset button. That or use a staple to short the lines by hand. ;)

I don't remember my reset button rig ever resetting the disk drive.
 

saundby

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Jul 21, 2009
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The Villages, FL, USA
I wired a debounced switch with a one-shot to my cartridge port traces on one system, a bare switch to the same traces on another, and used an artfully bent paperclip on a third. None ever had a problem (I'm still using the last two, the first got built into a test rig I don't have any more) but I don't think I'd go with a paperclip now--that system has a cartridge port expander with a real switch today. ;)
 

Raven

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I don't really understand the benefit of a reset button. I understand why things like the Final Cartridge III had them, it's one more selling point with almost no effort, but what's so much better about hitting a reset button than turning something off and on, especially on a C64 where the machine is the keyboard so the power button is literally by your fingertips..
 

carlsson

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A reset button will retain almost all the RAM contents, so you can recover from a crash. Powering the computer off and on will clear the memory completely.
 

Raven

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So a reset button kinda just resets the CPU when it has halted? That's interesting.
 

marc.hull

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May 26, 2007
Messages
107
Most electrical/electronic failures occur at power up. It's a matter of trying to extend to life of old brown. And hacks are cool as well reguardless of complexity ;-)
 

saundby

Experienced Member
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Jul 21, 2009
Messages
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The Villages, FL, USA
If you power cycle, you should count ten (at least) between power off and power on. A reset switch lets you get the same effect without the delay. Plus an intact memory, as said before.

When coding, I'd write with Merlin 64 and test with a HesMon cart. Having a reset switch when ML code is wonky is very useful.
 

carlsson

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Another case of when a reset button is handy is if you have some resident code in high part of the memory, beyond what many programs use. For example "Turbo Tape 64" relocated itself to SYS 50000 [$C350] which meant after loading a game with the turbo, you could often hit the reset button, type in SYS 50000 and the turbo was reenabled and ready to load the next program. Of course if the loaded program extended beyond this address you would have to reload the turbo program from tape or disk.
 

MrRobot

New Member
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Mar 24, 2010
Messages
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Finland
I used the reset button when my poor efforts at assembly programming locked up the machine. Hit the red button and sys 32768 and I'm back in TurboAssembler. All other resident programs would still be there, like a tape turbo, but by the time I had hacked my machine with a reset button I was using only the disk drive. Best of all, you'd keep on hacking the night away without having to reload your source.

Another use would be to enter cheats to games, which came as POKEs to various locations in memory to give you infinite lives etc., with a SYS call to restart the game.

No to mention the ubergeeky coolness of a hardware project even a blind monkey could do. :)
 
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