Floppy disk to USB adapter

[CountOmega]

Hi all,

I want to build an adapter for a 3.5" floppy disk drive. I intend on using the WD37C65 as floppy disk controller and the PIC32MX250F256H as microcontroller. I did already the circuit and wanted to hear your opinion on it. I know there are USB floppys for 20$. This is intended as a freetime project where I can learn something. I would really appriciate the input.

Cheers

Count Omega

 

[FvM]

It's surely possible, but...

You might reuse existing USB mass storage device code from Microchip software libraries. Writing the mass storage device framework from the scratch is a kind of nightmare. The floppy disk part is a bit simpler, but there's probably no read-made Microchip code.

 

[CountOmega]

Thanks, I know that I can use PMP to transfer the MFM encoded data onto the USB bus. What can you tell me about my circuit? Would it work this way?

 

[CountOmega]

So I did an update, improved e.g. the ICSP header. What do you think?

 

[KlausST]

Hi,

K5, K6: AHC driven with 5V supply can not reliably work with 3.3V (supply) input levels.
--> power them with 3V3 (my recommendation) or use AHCT type logic.

K2: one output is active in either case. be sure to prevent short circuit. To be safe: either use the IOE input or install series resistors.
(IOE: a pullup and two schottky diodes: one cathod to PMWR the other to PMRD could work)

generally: don´t leave any (unused) input floating. Neither analog nor digital.

No need to RESET the floppy driver IC? A port pin may be used or you may connect it to the PIC_RESET.
Btw: PIC is 3V3 powered but RESET is 5V level. Is this O.K.?

Is it O.K. to leave VUSBV3 and VBUSON not connected?

K3 should work. ..But any AHCT buffer will do, too. Single 5V supplied.
And it´s swapped in direction (referred to K2). No problem, but not very nice, too.

Klaus

 

[CountOmega]

Thank you for your reply. I have realised these improvements, and did some changes as to address the registers (K5).

No need to RESET the floppy driver IC?

A soft(ware) reset is possible via the µC.

Btw: PIC is 3V3 powered but RESET is 5V level. Is this O.K.?
Is it O.K. to leave VUSBV3 and VBUSON not connected?

As !MCLR is a 5 V tolerant pin this is ok, I think. If you don´t build an OTG device you don´t need them.
Improved plan is attached.