To preface, the establishment I work at has a recurring "Free Play" event.

As we have a number of games to sort through in the arcade, I began to think about possible solutions for reducing the amount of labor involved. While you can easily go through game settings and change the machine to "Free Play" mode, there's still a lot of churn involved.

The ultimate goal is to be able to set any/every game, regardless of manufacturer or type of machine, to a "Free Play" or coin-op mode remotely. Insert relevant buzzwords here. (IoT Pinball! Woo!)

I'm working out the low level hardware before implementing the controllers and developing the software stack.

What's involved in the WPC implementation is rather like what I've done with older Bally -35's: I use an EPROM twice (or more) the capacity of the original, program a it with a combined image of a normal ROM and a free play only ROM, run the most significant bit to the middle pole of a switch, and put the other switch poles on GND and VCC. This will be replaced with the appropriate control circuitry at a later point.

The difference between the Bally and the WPC implementation, though, is all in the software stack.

The first thing a WPC MPU does on cold boot is check the EPROM's checksum, then the ROM revision against what's previously stored in memory. Checksums can change out just fine on this platform. It's quite easy to calculate a new one after modifying the ROM image to set the boolean "Free Play" / "Home Use" bit to true. The check that matters the most is the revision label, which will most likely need to be forged.

You see, if the revision differs from what's stored in memory from the previous boot, a factory reset will occur. This isn't what we want.

I was able to generate a "Free Play Only" ROM for Fish Tales rev. L-5. Upon boot I found it running L-38, which was derived from the checksum. Ended up forging the revision label.

As a test rig, I took an Atmel 27C080, burnt it, then bent out the MSB (A19, Pin 1) and attached a toggle to it between VCC and GND.

The '080 was programmed with a concatenation of both ROM versions. After physical modification of the EPROM, it was then verified with both images using the '040 HI/LO bank toggle in the programmer.

After the forgery, Fish Tales stopped factory resetting. Both versions claimed L-5 with differing checksums.

What I ended up discovering is that you can change the "Free Play Only" bool on the fly. You might have to wait for the current frame to finish, but the next one that displays credit status should reflect what setting you have.

The resulting behavior is exactly what I anticipated and is a great stepping stone to full automation. While I can solve a lot more of this with modifying the game's code, this is a simple and realistic solution that's quite efficient in its implementation.

Now on to writing a ROM patching toolset for this...

_{Post edited by misentropy: clarification: poles.}

Video update:

I've coupled an ESP-01 Serial-to-Wifi module with the EPROM. Pretty happy with the results.

First off is the pricepoint. Card swiping systems are a huge investment. There's a bit of lock-in with having to purchase more cards over time. Lots of infrastructure. It makes a lot of sense to go this route if you don't mind eating a giant cost outright when you have more than a handful of games.

These wireless modules are cheaper than dirt. Average price is $2.50 per module.

This module could easily integrate with the coin switch line and provide a similar function using digital wallet systems, such as bitcoin. Already in the works

The MPU isn't modified at all. What you see is plugged directly into U6 with minimal modification performed to an 8Mbit EPROM (Tapping +5V, GND, and A19).

The methods I described as far as swapping different versions of ROMs should be somewhat universal with the WPC boards. This could be expanded to allowing one to choose a different ROM revision, or the free play only option, et cetera. Obviously this will also work in the arcade environment as well.

WPC games use 1Mbit through 8Mbit ROMs. Adapting a 16Mbit ROM isn't that big of a deal.

I'm quite comfortable patching WPC games to home use / coin-op; see the original post && https://pinside.com/pinball/forum/topic/jd-announcing-l1ah-a-coin-op-version-of-the-deadworld-mod.

$20 + S&H for a $0.49 micro and $0.35 in block terminals?

There's a difference between toiling and having fun with a hobby; pushing boundaries of what's known, what can be done with existing hardware limitations, and how to expand upon an outdated platform with modern components.

No, it's not the best idea ever. But at least it worked!