Re: PC as 1541

From: Gábor Lénárt <>
Date: Tue, 26 Apr 2011 22:38:28 +0200
Message-ID: <>

On Tue, Apr 26, 2011 at 09:04:07PM +0200, Spiro Trikaliotis wrote:
> The problems are different when using the PC as a IEC controller
> (connecting a 154x TO a PC) instead when using the PC as floppy drive.
> In both cases, there is the problem with the "listener hold off" (cf.
>, second question). This one is
> solved with the "multitask cable(s)" XM1541 and XA1541.
> OTOH, a IEC drive must react to an activated ATN within 1ms, or the
> controller (the C64, C128, or whatever) will miss that it is connected.
> 1ms seems like a long time; unfortunately, with a multitasking OS, it
> can be tricky to achieve this. That's why a DOS only solution is much
> easier here: You have control about the exact timing.

I am wondering if it's possible to use ATN line then to generate an IRQ on
the PC side (so you don't need polling).  This means the need to write a
custom driver then of course, but maybe it can be done then using a more
modern OS (I am thinking about Linux, anyway I wouldn't try to write a
device driver for Windows ...).  However I am still not sure, it can be
garantueed even with IRQ on the PC side to have that 1ms, and since I don't
know deeper thing on IEC protocol, I am sure it's not just this simple as I
imagine ...  (I only know that damn IEC ATN wire, I can't solder to the DTV
board only at the n'th time ....).

Honestly, since the need of parallel port, MSDOS, etc, I think the way
should be followed to use some kind of uC at least, which is a much
"comfortable" solution and no need to have "extra" stuffs like a PC running
DOS ... I know about projects like 1541-III, SD2IEC and such. However, I
still think I don't want to "fight" with memory cards etc, when my goal is to
use PC "as the drive" but in a modern way, let's say via USB connection.

Is there any project like this? As far as I can see, the mentioned projects
by me are mainly focused on various memory cards (or connecting a real 1541
to PC again, just with USB), while I would like to use my PC as the data
source (of course it's acceptable to transfer at least some parts of - let's
say - the disk image to the uC, just I don't want to write/read memory card
on PC, change it, read/write with the CBM machine on the end of an 1541-III
or so, change it, etc etc ...).

Some cross-development projects would need this for me, that I can easily
access data from both of C64 and PC but using no special software on the C64
(or DTV) side. For this, I think the best solution is to use the PC as the
1541 itself, that's the reason of my whole thread here.

> BTW, the 1541EMU uses another trick: It helps with hardware, using the
> same "ATN trap" as present on an original 154x, 157x or 1581, using an
> XOR gate. This way, the floppy drives reacts almost instantly to the
> ATN, and the PC/the floppy can take as much time as needed in order to
> react on it.
> (Yes, even the 1541 can have problems reacting in 1ms to the ATN. This
> is the case whenever the floppy has a long task to do in the interrupt,
> for example, when formatting a disk.)
> I hope this clarifies things a little bit.

yes, thanks for the information

- Gábor

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Received on 2011-04-26 21:00:13

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