I spent some time on the project last night. Still no-go.
The SX and the software is behaving as expected by responding to commands, transferring the buffer, so and so forth. I’m getting garbage data from the floppy drive. I put a scope on the floppy, and the data indeed looks screwed up. Last time this happened, putting a pull-up resistor on the data line fixed the problem. I have 1K pullup in place now, which is correct according to the specs I’ve read. Small cable, only 2ft long, well within the 1 meter specs.
Changing the value of the pull-up really seems to affect the shape of the incoming signal. I tried several different values from about 700 ohms through 4.7k. While they did change the shape to what looks normal, the time between edges is way off. In some cases, the time is way too short. In other cases, its excessively long.
What’s odd is that if I pop out the floppy disk, I still get a stream of output data from the drive. Where’s this data coming from? What is this data?
I have connected the DATA READY lead, and wait for that signal to start accepting data. This drops as it should, a short time after the motor lead goes low.
Speaking of motor leads, my floppy drive spins constantly as long as there is 12v applied. The spinning of the motor is *not* attached to the MTRXD lead. As soon as there’s power it starts spinning, then, when MTRXD is dropped low, the red led activity light comes on, and the data starts flowing. What’s odd is that ejecting the disk produces not even a hiccup in the data stream.
I really wish that the drive would simply not send ANYTHING whenever the heads aren’t on the floppy disk surface. What’s the head picking up and transmitting when its not on the surface? I would expect NOTHING…..
I’m not even confident that the data I’m currently seeing from the drive is even real data from the disk itself!!
I took apart my floppy drive yesterday, and it looks like a regular PC floppy but with an add-on board to handle the BUS-nature of amiga floppy drives. Outside of that circuitry, there were OR-GATES, NAND-GATES, and a D-flop flop. I’m half tempted to say screw the amiga floppy and go straight a cheap (and much more easily available) generic PC floppy.