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RC2022/10 Halftime update! So many great projects: https://www.retrochallenge.org/2022/10/rc202210-halftime-update.html

Less than 2 weeks left until we start! Check out the projects so far: https://www.retrochallenge.org/p/entrants-list-202210.html

We were going have it in January, but why wait?! We are happy to announce RetroChallenge for the month of October 2022! RetroChallenge 2022/10 Theme Categories We have one theme category for this event: Endurance Challenge. This category will be judged and awarded separately from the standard...

That looks like a late model logic board, maybe even for an apple II+. Also, the power supply is a later one for Apple //e, not the original gold tone. I am not totally sure, but just my initial impressions.

Building a backplane bus based Apple II will be difficult because most of the components can't really be separated from the processor and system memory over a single bus. Many parts of the Apple II are designed to work closely together. Take for instance the interleaved access of the system ram...

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.

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

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!

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.

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...

Apple I came with 4K of RAM and video terminal built in though. This was a pretty strong selling point. $621 got you an Altair with a bunch of lights and switches, and you still had to buy RAM at $338 for 4K!!

I figured! I would guess the 74ls251 too because it is an unbuffered digital chip connected to an external port. The 556 should be a little more tolerant of weird stuff getting plugged in. I could imagine a DE-9 RS232 cable getting plugged into the joystick port and sending 12V to the poor MUX!

Please let me know if you want any further help troubleshooting. Good luck!

As far as I know, the MMU is asserting (-) pin 18 when the keyboard address is decoded, enabling the keyboard data on the data bus. Most versions of firmware check if the open and closed Apple keys are depressed during the boot sequence to run a self test. Since the keyboard contains the...

Those are expensive EEPROMs. You can bring the price down a bit by using: https://www.jameco.com/z/28C16A-25-Major-Brands-IC-28C16A-25-EEPROM-16K-Bit-250ns-CMOS-Parallel-Refurbished_74691.html 250ns seems slow, but some of the Apple cards have 400ns ROMs, I think. And AT28c64 EEPROMs are dirt...

Don't people normally use a metal "nibbling tool" for this? They are pretty cheap on amazon (<$15) if you don't get any sellers.

Stan, Thanks for replying, I DM'd you!

I am curious if anybody has documentation on the MIKUL 6809-5 PLC boards? It is an EXORbus based processor card (like the Motorola EXORset, MEK6800D2, or MEK6802D5) made by TL industries as an industrial furnace controller. It is fairly unique for a PLC because it has an MC6847 Video Display...

But since we are guessing... I think Alpine car stereo full speed connector. It connects your ipod to your car stereo so you can control it using the stereo buttons. https://babcuvpisecek.com/diy/alpine-minidin-pinouts/

Ah yes. I thought "built in modem AND acoustic couplers built into it" meant you had 2 options. Doesn't it have RJ11 like this one?: https://www.digibarn.com/collections/systems/actrix/DSC02195.JPG I guess you could use an external acoustic coupler modem flipped around and laying on top! that...