[Coco] Floppies to PC or other OSs (was: Issues with 26-3022 interface)

[John E. Malmberg]

On 2/12/2013 9:26 AM, Daniel Campos wrote:
> Hi Mark,
>
> I understand your point, as this subject have probably been talked on
> this list many times over. But my main purpose is to pass disk images
> from a PC (through emulator or some other program) and run them on the
> Coco. I don't have any legacy 5 1/4 disks to worry about, so if I can do
> this work on a 3 1/2 floppy, for me is the best choice.
>
> I will try now to transfer some images from the PC to this disks and
> let's see how will it work...

Most typical 1.44 3.5 inch drives will work fine as a 720K drive in 
unmodified COCO computers.  That has been known for years.

Using 1.44 Media at 720 K is iffy, and your mileage will vary.

If you have Windows 98 or earlier, it is easy to implement a DISK 
utility to read/write coco disks with 256 byte sectors.  Several exist.

They also appear to exist for Linux.

With Windows/XP and later, Microsoft removed the API for setting the 
floppy sector size.

However, any unmodified COCO disk controller with any DISK basic ROM is 
quite happy to read and write 512 byte sector disks, as long as you have 
READ and WRITE verification off.

The BASIC routines can only access the first 256 bytes of the sectors to 
read and write, but you can access the rest with PEEK() AND POKE().

The trick is that the COCO allocates 256 bytes for read, 256 bytes for 
verify, and then 256 bytes for write and 256 bytes for write verify, all 
contiguously.

The COCO DISK ROM disk read/write routines do not count sectors, they 
just read or write bytes until the controller interrupts the computer at 
what ever the sector boundary is.  Since there is 512 bytes of buffer 
already available, it is simply a matter of transferring data in and out.

Which means that by playing some games with the bad sector table, you 
can probably have a PC or other device make a 512 byte sector disk that 
the COCO can do a directory of and read / write to.  You will only get 
1/2 the capacity of one side of the disk accessible from the COCO ROM.

It also means that you could write a COCO Basic program to read and 
write a 720K FAT formatted floppy if you were so ambitious, which means 
no special program on the PC.

Regards,
-John
wb8tyw at qsl.network
Personal Opinion Only