ruud.baltissen_at_abp.nl
Date: 2007-11-07 08:44:47
Hallo allemaal,
@Jim:
> You have heard of expansion part extenders, right?
Of course I have, I don't live in Far-away-istan :) But FC3 doesn't like
other cartridges parallel to itself. And I also have bad experiences
with the switchable expanders.
And to return the ball: I have heard of expanders for the Userports :)
> Sellam wishes to have a cart he can plug into the machines so
> they do not have to be booted by hand. Thus, they'll be a
> cart there anyway.
Nope, no cart needed. Somewhere in the '80s I saw an ingenious solution
in a 64er magazine: replace the original ROM with a 27128 and connect
A13 to the cassette port. The C64 starts up with the software in the
upper part of the ROM, does what it has to do, copies a bit of ML into
RAM and from there it negates A13 of the 27128 and does a "JMP ($FFFC)".
Regarding this upper part, it could load more software from a drive and
even better, it could tell the C64 to load its software from the
network. In this case you only have to maintain the boot software at one
place.
And of course we are not limited to use a 27128 only. Replace it was a
Flash tahta holds all the needed SW and when needed, it can update
itself over the network.
Regarding the automatic boot: using UTP we can reserve one line for
telling the system that the network is alive by pulling it High. The
first C64 to be started sees a (H) on this line and waits for its
masters hand to tell it whether to start up the network or not by
negating this line. All other C64's that are connected then see a (H) on
this line and will automatically start the network software. You don't
want to use a particular C64 on this net? Simply disconnect it. OK, it
will assume that it is the first one on the net and thus awaits your
input but that is a small price IMHO.
Why (H) and not (L) you may wonder? I'm thinking of a system where this
(H) powers a small electronic system that on its turn powers up all
connected computers: a wake-up-on-LAN function I mentioned yesterday.
The most simple thing that comes in my mind is a relay that switches the
power supply for the C64 to "ON".
> It seems a token passing or some other collision
> avoidance scheme is needed.
Using a token is the safest way but it also means that in one or another
way the C64 has to watch the network all the time to be able to pass the
token to the next C64. And if someone is running SW that disables the
network SW in some way, the token passing is stopped and the whole
network down. Using a master could solve this problem but that means an
extra C64 doing "nothing".
Only using up to, let's say, four computers, I would use collision
detection, Just as David described. But using five or more computers I
would start thinking of using a Master.
@David:
> The address could be encoded in hardware with dipswitches
> on the userport parallel lines.
Use a 74166 (I think), a parallel-to-serial converter. Only one clock
and one input needed. Two 166's and you have up to 65536 addresses. And
still only two lines needed. Would fit on the cassette port as well.
KISS :)
--
___
/ __|__
/ / |_/ Groetjes, Ruud
\ \__|_\
\___| URL: Ruud.C64.org
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