[sebhc] diskette drive

Patrick patrick at vintagecomputermarketplace.com
Sun Jun 6 13:23:20 CDT 2004

> The NEC 765 is easy to use hardware-wise; it doesn't take many chips to
> interface it. But, since it was never used in the H8, H89, or Z100
> series, this means you're going to have to write all your own CP/M and
> HDOS software to support it.

That's not so bad--I've written many a "BIOS"/driver for the 765 and it's

> Also, the 765 (as well as all the other floppy disk controller chips)
> are out of production. Finding any of them is a challenge. You may be
> reduced to buying them surplus, or scrounging them off old PC boards.

The spirit and function of this chip persists in many modern "Super-I/O"
implementations like the SMC FDC37669 and the National PC87322.  These are
readily available and implement essentially the same interface, with the
added benefit of a couple of serial ports, a parallel port, and an IDE
interface.  It takes some glue, no question, but not that much.  Howard
Harte has done such a board for S-100 systems, and it's a real beauty.  He
also added user-accessible Flash and a couple of other tricks, so it's a
really nice addition.

On the issue of DMA and/or use of polled I/O and processor speed, I assert
that a clever designer would simply have an on-board RAM buffer that the I/O
chip can read/write directly during DMA, and that can be separately
read/written by the 8080 or Z80 through either memory mapping or I/O ports.
Let the DMA happen as fast as it can, and let the CPU read the buffer at its
own pace after the board signals that the DMA has finished.


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