Mystery card/hack..Need help ID'ing!

[JSR]

Just purchased a Darth Vader Apple II, and it came with this unusual prototyping board. The unit came with a Disk II interface card, and a Language card.. this card is mounted near the language card.


It has not shipped to me yet, but I'm curious what this card might ne for.

There is a single chip with a single resistor, tied to what appears to be a toggle switch mounted directly on the card. Any idea what this might be?

 

[MacFly]

These photos don't really help. It would have helped to add a photo of the top side (so we can read the markings on the IC) and a photo of the bottom side (so we can see how the IC and switch are wired to the slot).

 

[JSR]

These photos don't really help. It would have helped to add a photo of the top side (so we can read the markings on the IC) and a photo of the bottom side (so we can see how the IC and switch are wired to the slot).

Best I can do for now.. those are cropped from the seller's listing, not photos I took myself. Once the unit arrives, ill be able to get some better shots of it.

 

[oldpcguy]

It will be interesting to see what the chip is so we can theorize what it might be used for.

 

[NeXT]

One inward-facing toggle switch, one resistor and one IC on a Apple II compatible protoboard.
It's not going to be ram or ROM or really anything complicated. My guess is it's altering the bus for some other device or it's just a junk card someone threw in?

 

[snuci]

At least it looks like it's on a genuine Apple Computer Inc prototyping board. That makes it a little interesting. Here is another for comparison.

 

[epooch]

There is a wire to the bus that appears to go to pin 21 (RDY) or 30 (IRQ), either of which could be useful to modify with one IC and a switch.
IRQ: could be used to generate regular timed interrupts every n cycles for a specialized application. This was a feature sorely lacking in the Apple II and necessary for most operating systems.
RDY: could be used on the RDY line to slow the processor down for debugging, or single stepping. You probably need another switch for that though. Here is Woz's original single IC circuit for that function:

http://www.bitsavers.org/pdf/apple/apple_I/AppleI_Manual.pdf#page=12

It is hard to know for sure without knowing the IC, but a single stepper seems likely.

 

[JSR]

((Unsolved Mysteries music))

UPDATE!

The system arrived an hour ago..I pulled the card, and photographed it extensively.

The chip is a TI 74LS74AN flip-flop. It is indeed an Apple badged prototyping board..! But what the hell is it doing?

Pictures:

 

[epooch]

Looks like it sends an NMI when the switch is flipped, and resets it when the switch is reset and flipped again. Good for debugging or cracking.

 

[JSR]

Looks like it sends an NMI when the switch is flipped, and resets it when the switch is reset and flipped again. Good for debugging or cracking.

Aha! So, a snapshot sort of card! A little bit of early sortware piracy history..?

 

[epooch]

It is hard to see how pins 2, 3 and 4 are connected. I think it just pulls NMI low in one switch position and high in the other position. Hard to tell, but I dont think you even need an IC to do that!

 

[JSR]

I noticed this is an Apple branded prototyping board..who would have made this? An Apple employee?

 

[epooch]

No, they were sold pretty widely as the Apple II hobby prototyping board:

https://bespin.federalproductions.com/mycloud/Apple%20%5D%5B/Apple%20Computer/A2%20Hobby%20Prototyping%20Board.pdf

 

[MacFly]

It is hard to see how pins 2, 3 and 4 are connected. I think it just pulls NMI low in one switch position and high in the other position. Hard to tell, but I dont think you even need an IC to do that!

The flipflop's set and reset inputs are each a wired with a 1K pull-up resistor. The toggle switch connects either input low. So it either sets or resets the flipflop.
The flipflop output is directly connected to /INTIN (slot pin #28), the normal interrupt input. So, yes, this was a simple device to trigger a normal interrupt (not an NMI, but the normal IRQ).

Indeed the flipflop would not really be necessary to trigger the interrupt. The switch could have been wired to the interrupt input directly. But the flipflop acts as a debouncer. Generates a clean interrupt signal - even if the switch briefly bounces when flipping it to the set or reset position.

 

[epooch]

The flipflop output is directly connected to /INTIN (slot pin #28), the normal interrupt input. So, yes, this was a simple device to trigger a normal interrupt (not an NMI, but the normal IRQ).

That definitely looks like pin 29 ( /NMI ) to me. I think you are maybe skipping the ground finger at the back. INTIN would not generate an interrupt since it is N/C to anything except the INTOUT of the lower card slot, which should be an output.

 

[MacFly]

That definitely looks like pin 29 ( /NMI ) to me.

Yep, you're right, it's pin 29/NMI. Seems I was counting the holes and indeed skipped the ground pin.

 

[MacFly]

... and the "mystery card" is now for sale on fleebay. Part of the B&H system. Yours right now for US $3,925.00. Quick!

RARE! Early Vintage Bell & Howell Darth Vader Apple II w/ Tape and Disk Drives | eBay

Find many great new & used options and get the best deals for RARE! Early Vintage Bell & Howell Darth Vader Apple II w/ Tape and Disk Drives at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[VERAULT]

... and the "mystery card" is now for sale on fleebay. Part of the B&H system. Yours right now for US $3,925.00. Quick!

RARE! Early Vintage Bell & Howell Darth Vader Apple II w/ Tape and Disk Drives | eBay

Find many great new & used options and get the best deals for RARE! Early Vintage Bell & Howell Darth Vader Apple II w/ Tape and Disk Drives at the best online prices at eBay! Free shipping for many products!

www.ebay.com

and its RARE too, they must have only made 1 or 2 of these and not mass produced 10s of thousands of these things. If it says RARE on eBay it must be true. Steve Jobs Steve Jobs...