Hello Ricardo,
GV>I've made an EPP (Enhanced Parallel Port) interface to link
>the SV with my PC,
>
RJ> Greg, you've done a EPP interface 4 your MSX, isn't it? Excuse
> my ignorance, but it works like a EPP in a PC? I'm asking it to
> you 'cause it's a very interesting project. Here in Brazil we
> were talking about connecting PCs and MSXs into a LAN, maybe
> using the NetBIOS or TCP-IP protocols. So, someone talked about
> creating a EPP 4 MSX, and connect an old parallel port LAN adapter
> to our MSXs (these LAN adapters can be found at very low cost here
> in Brazil). Of course, an EPP 4 MSX could have many more
> applications than just a LAN adapter...
> [EMAIL PROTECTED] - [EMAIL PROTECTED]
I hope you won't mind that I reply via this public list, so that
this information is available to others interested in EPP...
I've made an EPP interface for my Spectravideo SV-328, which has
the same CPU, VDP, and PSG as original MSX -- but its i/o mapping
is different. I'll eventually port the circuit and code to my MSX
Yamaha CX5M.
The EPP Specification covers a core of hardware signals, but is
otherwise open to interpretation; nothing is said about software
protocols. EPP supports one "master" which must be involved in
all exchanges of data with devices on the EPP channel.
There are gaps even in the hardware specification. For example,
an EPP device can cause hardware interrupts at the EPP master,
but there's no specified way for a device to first check if the
master is ready to accept a byte transfer. There's no specified
way for the master to know which device is asserting the one
Interrupt line, or asserting the one Busy line -- it could be
a fast EPP device or slow SPP (Standard Parallel Port) adapter.
This could potentially bog down an EPP channel/network using a
mix of new/fast & old/slow parallel-port devices -- unless some
of the EPP devices are micros (e.g. MSXs) that act as "servers"
to old SPP devices -- such as LAN adapters -- attached directly
to them, thus providing localized buffer/spool capability.
For multiple devices, the simplest software protocol would use
something like token-passing or round-robin polling, where the
master gives each device a chance to speak. There are separate
EPP Data-Strobe and Address-Strobe signals, so a device could
know when the master is specifically addressing it.
Not all EPP hardware implement all features, nor the same way,
so there'd need to be agreement of a specific set of circuits.
My Pentium PC hardware assumes the role of EPP master, so my
circuit and code interface my SV-328 as an EPP device.
Greg_
http://www.netcom.ca/~telic
98.Sept.10, Toronto, Canada.
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