Re: 1551!

From: Levente Harsfalvi (
Date: 1998-09-06 16:31:40


> Alright guys, down to business. Guess who found a 1551 disk drive
> yesterday? :-) That's right, in its original box with manual and
> diskettes. So far I have been unimpressed by its so-called "speed", but
> perhaps that's because I'm used to 1541 fastload routines such as Datel's
> Action Replay.

There are a lot of native 1551 fastloaders, just ask Crown or Csory
about. (...Csory was one of the most known people who developed stuff
for native 1551 mode).

I also remember a disk backup util which copied a whole disk image (using
two 1551's) in 16 secs.

> So, the question is: how fast can the 1551 be driven? I had a brief look
> inside the drive (hmm, quite similar to the 1541C board) and the interface
> cartridge, and I can tell you that there are 16 (sixteen!) wires between
> the cartridge and the drive. So what are those mysterious coloured wires,
> and how can they help us? I figure it ought to be possible to get proper 8
> bit parallel transfers, rather than the standard 3 bit (why?!?) protocol.

The drive uses parallel data transfer of course. The 6523 TIA in the
plug gets mapped into the Plus/4's address space (the decoding is done
with the FPLA also found in the cartridge). The TIA has 8 + 2 + 2 port
bits, 8 lines are used as data, 2 lines as handshake and the other 2...
well, I don't know them.

(The data transfer is fully synchronised. The Plus/4 Kernal doesn't even
forbid IRQ while doing I/O between the drive and the machine.)

How fast could it be? ...Heh, you can estimate it :-). The drive has a
2Mhz 6510T processor, and more RAM than an 1541 does (if I remember it
right). You have a lot of lines, and speaking of the Plus/4, a computer
which may be tricked easier to achieve fast speed than a C64.



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