tep392

I added an FDC+ floppy disk controller to my system and connected my Percom drive (Atari version). I had to disconnect the Atari interface board and add a ribbon cable from the drives to the FDC+. The FDC+ is a modern replacement for the Altair FDC. It adds 64K RAM, 8K ROM and supports PC drives with soft sectored disks, as well as original Altair drives with hard sector disks. I spent some time last night copying disk images to floppy. Now my system is cooking! Dual minidisks, cassette deck, 64K RAM plus ROM with only a 4 slot backplane!

And it works!

My 88-UIO boards finally arrived from China.

Bump

Yes, that seems like an easy solution. Maybe the power usage was within the limits of the design requirement, so they felt no need to make it any more complex.

You sir are correct. A NIB still in shrink wrap 1020 sold on Ebay for $100 two months ago.

Great project! Coincidentally, I was doing something similar over the holiday's to reproduce a serial and cassette I/O board for the Altair 8800. I didn't have access to a bare board, but did have high quality photo's of the front and back to use. It presented a few challenges, but the board complexity is nothing like the 1450 you are working on. This was my first board design and I used ExpressPCB, which I will never do again. They will only give you gerbers with a board order, so when the inevitable corrections needed to be done, I had to modify the gerbers by hand. ExpressPCB is seriously over priced. I did learn a lot from the experience though.

Fixed it

For those of you who are interested in the inner workings, here are some images from the adjustment of the PLL. This is a Kansas City standard test signal (1200/2400Hz) with the corresponding digital conversion. I adjusted for KC standard. After adjustment, switching to MITS standard test signal (1850/2400Hz), and checking digital signal is good. The adjustment of the PLL is not the same for both standards. There is a bodge added on backside of board to switch in a parallel resistor when using MITS standard so that the trim pot doesn't need to be readjusted between the two.

Front side view. I used the board to read in the Altair 8k BASIC cassette bitstream and then write it back out to cassette using the KC standard. I had to write the copy program and key it in on the front panel. Some old school pirating there.

The MITS 88-UIO board is done! I had a couple bugs to chase down, but it seems to be working perfectly now. Here's a pic of Altair BASIC 4.0 loaded from cassette.

It is cool to see the 2600+ enabling some of those XM features. If the firmware gets to the point where it can support POKEY/YM sound, RAM and High Score Cart, then it will have the most useful features of the XM. I have four games, Beefdrop VE, Froggie, DK XM and PMC 40th that don't have sound chips in the cart and would benefit from those features. I wasn't planning to buy the 2600+, but seriously considering it now.

That is great news! Is this with the Beta firmware? I thought I read that it didn't have sound with the original firmware. Or maybe that was the PK version that someone tested. It's been to long for me to remember, but my guess is that I would have disabled the external XM POKEY when the chip was added to the cart for the PK version.

Already has been.