The Sinclair QL Forum

All I can think of its running all 8 MDVs at same time is a great way to generate a random number, not much good for anything else!

Since I don't need to run the protected version of West any more now I've repaired the original cartridges and tested them, and hopefully nothing else I need to repair spins up 8 drives, I've refitted vMap in my QL - Happy Days!

t0nyt wrote: Thu Feb 06, 2025 5:52 pm Just done more testing and vMap is preventing it _running_, so magic number was probably correct all along (which explains why when I imaged it back it worked in q-emulator still)

Interesting... I suspect it might be a vMap timing issue when the code to start/stop the microdrives runs from RAM rather than ROM.

Can you actually get more than one microdrive running at the same time?

At the direct sector access level, If you have more that one cartridge fitted, Which one gets read? or do they all get read at the same time, mixing up the data?

Is the Qemulator 'all drive lights coming on' just a Qemulator thing.

Hi!

In theory, it's impossible to get all MDV units spinning simultaneously - unless there is a fault in one of the MDV ULAs.

As for how QEm copes with unexpected COMMS CLK behaviour, I'm not sure.

Martin_Head wrote: Sat Feb 08, 2025 10:31 am Can you actually get more than one microdrive running at the same time?

As Martyn says, it's not possible.
At most, you could have some motors temporarily spinning at the same time due to physical inertia and capacitors in the circuit.
I think multiple leds can be on at the same time when cycling through the drives thanks to the capacitors, but only one drive can be selected at a time.

M68008 wrote: Sat Feb 08, 2025 6:28 pm

Martin_Head wrote: Sat Feb 08, 2025 10:31 am Can you actually get more than one microdrive running at the same time?

As Martyn says, it's not possible.
At most, you could have some motors temporarily spinning at the same time due to physical inertia and capacitors in the circuit.
I think multiple leds can be on at the same time when cycling through the drives thanks to the capacitors, but only one drive can be selected at a time.

What happens for real when you keep clocking 1's into pc..sel?

M68008 wrote: Sat Feb 08, 2025 6:28 pmAs Martyn says, it's not possible.

However, I can remember some spectacular crashes on the QL where both Microdrives started running.

XorA wrote: Sat Feb 08, 2025 8:02 pm

M68008 wrote: Sat Feb 08, 2025 6:28 pm

Martin_Head wrote: Sat Feb 08, 2025 10:31 am Can you actually get more than one microdrive running at the same time?

As Martyn says, it's not possible.
At most, you could have some motors temporarily spinning at the same time due to physical inertia and capacitors in the circuit.
I think multiple leds can be on at the same time when cycling through the drives thanks to the capacitors, but only one drive can be selected at a time.

What happens for real when you keep clocking 1's into pc..sel?

Good point, I was thinking about the ROM code and recommended code... if one directly sends a series of 'select' bits set to 1 and 'clock' bits, it may be possible, not sure.

It doesn't sound healthy, as the two MDV ULAs could then send data to the MDV bus at the same time. Hopefully there is some protection inside the chip.

Ah, yes, I too hadn't thought about the case when the COMMS DATA line is left active between pulses to COMMS CLK...

That's certainly possible - and naughty! On a real QL, it wouldn't take much to overload the 9v power line with a few MDV motors spinning concurrently.

As the actual RAWDATA lines are (or appear to be) configured in 'common emitter' mode - either sourcing current or left high-impedence - it shouldn't harm the ULAs directly, but of course the various common-bus signals (including MDVRW on the QL, with its curious but cheap/clever WP handling) would be rendered meaningless.

Getting a little off-topic, but an interesting thought...