Wednesday, December 23, 2009
I tested the DS0026CN chip last week. Although you can enter a program which the system appears to accept, displaying the bytes in memory afterwards shows completely different data. Why bother? Because the DS0025CN is pretty hard to find. I believe I paid $13 USD for a single chip!
Posted by John at 11:24 AM
Sunday, December 13, 2009
Wednesday, December 9, 2009
On Dec 8 at 1:15AM I finally had reset working and dropping into the monitor program. After building the keyboard circuit, I keyed in the test program from the Apple 1 manual. Eureka! Well, one board works (the one that came with the kit). The board I built from scratch components doesn't pick up keyboard events yet, so this board will need additional debugging. But as you can see on the board that works, the ASCII charset is being dumped repeatedly just like it is supposed to.
I started the night with building the Apple II keyboard -> Apple 1 mapping circuit based on WSander's mapping schematic. I did not wire up the Repeat -> Clear mapping yet (which requires one trace modification on the keyboard).
Pin 1 (+5v) on the Apple II keyboard ribbon cable was broken clean off, so I had to separate the wire from the ribbon. I did this with an Exacto blade. Then I extended it about 5 cm by soldering another piece of wire. I didn't have any heat-shrink on hand, so I had to use electrical tape to cover up the bare connections. This made the wire long enough to sneak it underneath and into the DIP socket. As you can see in the photos, I used 16 pin ZIFF sockets on each of the ribbon cables. I also added a DIP socket to each end of the ribbon cable to protect the pins.
One thing worth mentioning, as I am not that familiar with Apple II keyboards -- there is a switch on this particular 1979 model, underneath the keyboard on the encoder PCB. This switch has 2 settings: Ctrl and Reset. My keyboard Reset button did not work until I flipped the switch from Ctrl to Reset.
Posted by John at 2:56 PM
Saturday, December 5, 2009
All of the preceeding images were sent to me by W.Sander
I will be using Sander's design for my keyboard rig. He was kind enough to go out of his way to obtain the video signal images and a nice image of the Apple 1 screen when the system is first booted.
Note that the ampersand symbols flash, but the dashes do not flash. Check out the cool case for the Apple 1, also designed by Sander.
Posted by John at 3:02 PM
This is a shot of the clock signal on the 6502 / PIN-37
The peak is at 4 volts, and the frequency is 1.020 MHz. Horiz sweep is 500.0 ns.
I'm not sure why there is a negative spike in each cycle?
You can see the same spike in one of the photos below, on the analog scope taken from Clone number 1.
Posted by John at 3:50 AM
I started working on the second clone (the kit version) last night. I finished it tonite, and this one works. I haven't figured out what is wrong with the first one I built (the non-kit version), but I still cannot obtain any video.
The image above shows the PCB with DIP sockets, 22uF capacitors and diodes soldered into place. The resistors all came in one bag, so they had to be checked with a multimeter and sorted.
Looking at the image above this, you can see that this system is generating video. When I power up the board, I see a screen filled with flashing "_@_@_@_" symbols. I know that this is the correct behavior (An Apple 1 owner recently sent me this info). I don't have a keyboard hooked up yet, so what you see here is the expansion board I built a few months ago, being used to send a reset (recall that after you power up the Apple 1, you hit "Clear" then "Reset"). I don't always get the same results, but I am seeing the "\" and the "@" symbol most of the time after hitting reset. I believe this is correct behavior.
I decided to go ahead and test some of the chips I had laying around. I briefly swapped out the DS0025CN with a DS0026CN and I'm not 100% sure yet, but I think the DS0026CN might work. I need to play around with this a bit more to be sure. While I was at it, I also checked a few of the PROMs I had programmed.
I learned a few things while building this second board, and the first thing I learned was that .032 solder was too thick. I ended up using .020 63/37 rosin core on the second board (See video below). I really thought it was going to be too thin to work with, but it turned out to be perfect. I did use .032 on the components with larger PCB holes and thicker leads (e.g. the power regulators, and the big blue caps).
I also found that the first little PCB I built for the video RCA jack is messing up the signal. I suspect the LED, resistor and IN914 diode. The second board I put together last night works fine, but this one has no LED, resistor, or IN914 diode.
Posted by John at 3:18 AM