From: Baltissen, GJPAA (Ruud) (ruud.baltissen_at_abp.nl)
Date: 2003-12-09 10:20:21
Hallo Nick,
I'm sorry for the late answer but I accidently moved it to the wrong map and
only just noticed it.
> With 64HDD I have found you need to have support for 16channels
> (secondary addresses) for each device number, and keep track of all.
That's exactly what I do with CBM-HD as well.
> On the serial bus this is done by holding the DATA line active (low) and
> the C64 won't be able to send any new instructions until the internal
> operation is done, and the line freed
I have thought about this as well but the problem is that you then block
_all_ communication. With two 1541s the program
10 open 1,8,15,"v0"
20 open 1,9,15,"v0"
will let the Validate happen at almost the same time on both the drives. But
if device 8 is your PC and it lowers DATA, line 20 won't be executed until
the first Validate is done. I noticed this behaviour when having both my PC
and 1001 connected to my 8032.
But your remark is still helpfull because it made me rethink things again.
And I came up with the following idea:
I don't use the interrupt at this moment. But using it enables me to check
ATN independant of any action the PC is performing. So for example when an
ATN occurs during a Validate, I can read the byte telling me what device the
command is meant for. If it is one not supported by the PC, I can ignore it
and the rest. If it indeed is supported, I can block any further
communication by lowering DATA, or in my case NRFD.
> ... The parallel IEC bus would have a similar "hold-off" method,
> just not sure which signal line is used....
NRFD, Not Ready For Data
--
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