HxC Floppy Drive Emulator

I'm working on a project for a Spectrum compatible, the project is old (1986) and currently is quite lost. The floppy interface for it can work with 4 floppy drives at once. It uses individual SELECT, MOTOR ON and READY signals.

I'm playing with the idea of using the SD Card version of your emulator for this computer but I'm not sure about the meaning of the signals at its data connector.

For instance, is the READY signal on pin 34 really the same thing with the definition of the READY signal from the original Shugart SA400 standard (ON when disk inserted and spinning)? Because if it is, then that means the signal on pin 2 of your connector (DISK CHANGE) is not where it should be for those who want to use this emulator on a standard PC. On a standard PC, the DISK CHANGE signal is expected to come from the floppy on pin 34.

Personally I don't need the DISK CHANGE signal, and if pin 34 is really delivering the READY signal as per the original Shugart standard, then it's just perfect for me.

What happens in my case is that back in 1992 when I first used a 3 1/2" floppy drive with this computer, I had to disconnect pin 34 of the drive from where it was connected and hook it up to a switch that detected the presence of the disk in the drive. Otherwise said, I changed pin 34 of the drive in order to deliver an improvised READY signal instead of the DISK CHANGE signal.

Then there is another question: if you say your device can emulate 2 drives, does that mean it can emulate 2 drives being connected to the computer AT THE SAME TIME?

Because if so, I don't see two separate READY signals coming out of the emulator. And I strongly suspect your device CANNOT actualy work as two separate drives connected at the same time. At least not in the computer I'm building, which needs separate READY signals from each drive.

I'm just trying to understand what you did before deciding to buy this device, because if it proves to be useful to me, I will need 100 pieces, since I'm planning to build 100 of these computers.

The READY signal is available and shugart compatible. There is a configuration file in the emulator which tells it what to do, and it can be configured as a DISK CHANGE signal if needed, for use with a PC Compatible computer.

The emulator can emulate two drives, by answering to different "drive select" and/or "motor on" pins. How does multiple ready signals work for you ? On all computers I know there is a single ready line connected to all drives. I'd expect the READY signal for each drive to be active only when the matching "drive select" is active ?

Exactly : the behaviour of the pins 2 & 34 change with the interface mode selected.





What do you mean by "AT THE SAME TIME ?"
In fact it emulate 2 disk drives connected on the same floppy cable (the same FDC).
Of course with this setup you can access to only one disk drive in the "same time".
The drive to access is chosen with the DSx lines.

Yes, you are perfectly right pulkomandy, this is the standard behaviour. As per the Shugart standard, the drives receive separate SELECT signals and a common MOTOR ON signal and the drive selected responds by activating the common READY signal.

Later on, IBM changed things a little when they introduced the cable twist, at which point they introduced individual MOTOR ON signals for the two possible drives on the cable (so NOW that means separate SELECT and separate MOTOR ON)

Well my computer is even more detailed, its floppy controller has also separate READY signals. I'm attaching here the schematics of the floppy interface so you can see what I'm talking about.

I'm sorry, I just realized I was wrong when I said:

"Because if so, I don't see two separate READY signals coming out of the emulator. And I strongly suspect your device CANNOT actualy work as two separate drives connected at the same time".

Obviously, your device DOES comply with the Shugart standard from this point of view. What I should have said is "HxC may not work with my particular floppy interface because this interface uses individual READY signals".

But I just figured right now, if you look at the schematics on page 2, I could simply bypass the multiplexer U04 and use a common READY signal from all drives, right?

I only have one real question left: how can the HxC work if it ignores the MOTOR ON signal? If I'm not wrong the manual says:

"Unlike real floppy disk drive the SDCard HxC Floppy Emulator doesn’t use the
motor control line. So there are only one jumper to set per virtual disk drive."

So how can it work if it ignores the MOTOR ON?

Second: thank you for explaining, I didn't know the configuration file can actually change the location of signals on the connector pins. That is really useful !

And for Jeff: I meant "2 drives connected to the cable AT THE SAME TIME", that is the drives are connected to the same cable at the same time, but of course they will NOT be ACCESSED simulaneously, that's impossible, I realize that

So I guess the only question for me is: does SDHxC really ignore the MOTOR ON signals? And if so, how can it work this way?

Thank you all guys, I appreciate your assistance.

You can remove U04, since the drives are only forcing the ready signal to low level. When no drive is forcing it, a pull-up on the controller side will raise it high. This way there are no conflicts between the drives.

As for the motor on signal, the HxC acts as if it was always spinning, and relies only on the drive select pins to do the drive selection. Since there is (almost) no spin-up time for the SD card, this should work in most cases, unless you have very tight timing constraints related to the motor on signal ?