From: André Fachat (
Date: 2000-10-22 19:14:58

Sorry to jump in so late only, but I am completely under water with work.

Just one hint: The VICE emulator contains a complete IEEE488 state engine
that is used to monitor the IEEE488 lines of the emulated PET and CBM2
(and C64 weith IEEE488) computers. I detects the state of the bus from
the transitions of the IEEE488 lines. At the right times it fetches bytes
from the virtual drive emulation (when a 2031/8050 etc is not truely 
emulated.) resp. puts a byte there. (One catch there: the drive emulation
must buffer the last byte sent as the transmission can be interrupted
by the PET by sending an UNTALK)

The engine is tested against all the IEEE488 fimrmwares I know (several
models, CBM2 and C64 and VIC20 IEEE488 expansion ROMs. It is also used
in my IEEE488 interface for the PC printer port (based on your
original ideas, Ruud!)

The file in the VICE emulator is called "parallel.c" as far as I remember.
You might want to have a look at it.

Hope this helps and so long

The file is c

> On Fri, 20 Oct 100 wrote:
> > > 
> > > There is an end of transmission signal sent from the drive, apart
> from the
> > > IEEE protocol, that indicates that loading has terminated.  I am not
> > > familiar with what that actually is....
> > 
> > That is the EOI-signal which is a sepperate line on the IEEE-bus. The 
> > EOI-signal on the IEC-bus is created by fiddling around with some
> timings.
> > 
> > The bytes where I am talking about are $48 and $60 which appear after
> the drive 
> > has sent two or three bytes. Why is the computer sending these bytes?
> Why do 
> > they appear in the middle of the transmission of the third byte? A
> little bit 
> > further you se the C= transmits a $5F, Untalk, as well. Why didn't it
> earlier?
> I don't know why the drive is sending extra bytes, but it clearly does
> and
> this is allowed for in the load routine.  These bytes are ignored and
> the
> computer waits for an EOI.  While it is waiting, the status byte must be
> kept valid, i.e. set as valid data received and not timed out.  Part of
> the wait loop is to set the status read error off each time through the
> loop.
> I see also that the "Tool Kit" book says the computer sends the untalk
> as
> a substitute for an EOI from the computer.  On the IEEE drives, you may
> have to send an actual EOI from the computer.
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