Speed Cart 64: Slow Down Your Commodore 64, Sometimes

If you've ever found your Commodore 64 runs too fast, maybe you need a Speed Cart 64 which provides a way of slowing down the C64. Sometimes. Sometimes it actually speeds things up, and sometimes it glitches programs in bizarre ways. And sometimes it just crashes.

To support 8-Bit Show And Tell:

Extra thanks to:

Index:
0:00 The Speed Cart 64
2:05 Slowing down 10 PRINT
4:14 Testing some games: GORF, Jupiter Lander
6:36 Jumpman Junior, Mountie Mick's Death Ride
11:20 Bruce Lee II, Wizard of Wor
13:53 Examining effect on the TI (jiffies) variable
17:25 Bremse 64 (Brake/Break 64)
18:08 I attempt to explain the circuit...
24:17 Potential improvements, clarifications
26:05 Thanks to my patrons

[Darxide]

"This is my favorite game about a Canadian Mountie."

Such a competitive genre. How can you choose?

[diamondsmasher]

“My favourite game about a Canadian Mountie.”

Uh…. right…. Much better than all those OTHER games about Canadian Mounties ;)

[markjreed]

at 4:00 the line "Very irregular flash" gave me visions of Barry Allen making lots of super-speed trips to the bathroom ...

[jimbrain]

Yay! I got a greetz (I get so few...) I *think* I know why they used a TTL IC. Well, we all know they used this design because it was cheaper than other options, but it is cheaper in a slightly tricky way. The goal is to provide a way to optionally slow down the 64, for whatever reason someone wants to do that (I won't judge). The sensitivity of the design allows the same circuit to do three things. Create a constant IRQ (when turned counter-clockwise, the input is ~0V, and this means the IRQ is always held low, which is not useful), create a variable cycling rate for the IRQ (the good part), and create a constant lack of IRQ (in essence, the unit is off). Without that 3rd behavior, the design would also be creating IRQs at some frequency, no matter how slow, and a switch would be needed to turn the unit off. Thus, the temperamental nature of the circuit and the fact there is a region where it will not create an IRQ was used to cheaply create an "off" mode.

[jpcompton]

(I see what you did there with the credits)

[bengmo]

If I've learned anything from YouTube, that potentiometer might need some deoxit

[the_eminent_Joshua_E_Hrouda]

Adding a plastic knob (the bigger, the better) to that pot would give you A LOT more control over it!

[DavidYoud]

@8:50 "This is my favorite game about a Canadian mountie". Wait, how many mountie games are there?
@26:15 hahah, nice (interrupted roll call)

[francoisleveille]

Funny! That's exactly what I did with my VIC-20 15 years ago. A 74HCT161 connected to the RDY line if I recall correctly.

[anovaprint]

I'm just now learning about TTL chips so this was extremely useful.

[LordRenegrade]

There's a lot of people using Raspberry Pis as various Amiga accelerators, flickerfixers and SCSI boards - I wouldn't be surprised to see someone use a Pi Pico in the place of a 555. I'm sure it could read a potentiometer and output appropriate number of pulses - scaled better than a raw pot too...

[BitNaptime]

If a cartridge could make the 64 slower, Commodore would have developed it in the '80s.

[PlasticCogLiquid]

I'd like to hear more SID's slowed down. Like Agent X II

[EmilOppelnBronikowski]

That's the most compact version of 10 PRINT you ever wrote on this channel. ;-)

[pollyisagoodbird]

So would this be useful if I were to run PAL region games on an NTSC system? I hear you can, but they run faster than they should

[csbruce]

0:12 How does a Commodore Security badge make your computer faster?


2:59 You can accomplish a similar thing by POKEing the high byte of the IRQ timer.

4:30 Won't the game get very confused if it uses raster interrupts? This is probably one of the things that happens to your favorite Mountie game.

13:52 I was spoiled by the schematic diagram in your (original) thumbnail!

24:34 NMIs wouldn't be feasible. The thing about NMIs is that they're *Non-Maskable*! If they're generated too quickly, they interrupt each other until the stack wraps around and garbles itself. I ran into this problem with SwiftLib @ 115.2kbps. The advantage of IRQs is they don't produce nested interrupts. Places where the system appears to pause with the current device (from a new IRQ being initiated immediately after the preceding one completes) would see the NMIs overflow.

[steviebboy]

I remember having a cartridge for the Commodore Amiga, Action Replay revision 3 if i remember correctly and it had a pot on there and you could slow the machine down. But it has been so long I cant remember how well it worked.

[mechaform]

I absolutely loved Jumpman Jr.! Many a pleasant hour spent with that title.

[mikerobertson]

It could also be useful for debugging too. Seeing exactly where on the screen a glitch occurs, abit like stepping through now with VICE using ALT/+ (or SHIFT/ALT/P on newer builds)

[soundcheck]

Even if they didn't want to pay for a 555, they could have built a much better voltage controlled oscillator using all 4 NAND gates on that chip. Alternatively, this simple circuit will work better if a resistor is added between the output of the first gate and ground.