> Rather than parallel why not SPI as implementing that is far simpler.
> hard ware needed is an out put bit and input it and a birdirectional
> clock.

Yes, you can do that even directly with the WIZnet Chip, it can work
in SPI-Mode. But you would need the same on the Z80 side - I have not
a SPI-Interface in my Z80-System but I have a so called Digital In/Out
Modul ready for such experiments and a PIO is simple enough for me.


> There are a few PICs and other chips that can do the bottom layers of
> the stack to the media level and save a great deal of low level
> software. Also there are Ethernet chips that will do the work all the
> way to packet buffereing so that the host doesnt have to be fast to
> do the higher level work.

Yes there are some very interesting projects, like http://www.sics.se/contiki/
or some implementations of software stacks with microcontrollers here:
http://members.home.nl/bzijlstra/

Why used Ben the same Chip for the newest project "Red Bokito" - it is
very simple to program and it works like expected, in my Interface
too. What the controller makes with the chip I can do with the Z80 in
the same way, all what I need is a simple and fast bridge to program
the stack with Z80-Assembler, my prefered language. This makes the
KCNET possible for me in my system now.

> I don't know about most systems referrcences but most of the common
> hard ware here are 4mhz Z80 and that can if pushed move around
> 50-60Kbytes/second.

Yes, now limits my 1,75MHz - System the speed, I think you can reach
about 50 kB/s with a 4 MHz System if the ATmega (my bridge on the
other side) can handle this. I can't test it.

> If the device has the Z80sio/dart those can run
> serial to 56K

The 56K are kBit not kByte.

>*Going
> parallel will not gain much speed over that. *Its a matter of CPU
> speed and cycles needed to do transfers.

I think it is a difference between 56kBit and 448kBit or 7 kByte and
50 kByte, by the way, for usability you need a minimum of about
7...10 kByte/s, this is my personal experience so far. Thats why I
prefer the parallel hook of the interface.

> However if the eithernet inerface can buffer packets so that the

host
> runs at it's speed it will work smoothly and can even "feel"
> responsive.

That is not enough, the handling of the packets between the layers of
the stack and TCP-Handshake for example is a time consuming and tricky
issue - all done by the hardware stack from WIZnet, I can and must do
only the rfc protocols in the Z80-system.

DHCP - I can't follow the send - receive messages of the client on my
screen, its to fast

TFTP - the data packets with the filedata are so fast, that the hdd
can't write them

PING - here you work on the IP-layer and must calculate the IP-
checksum on the host (Z80) for incoming and outgoing PING-Messages and
measure the time from send to receive - the time has a deviation of
100 ms, when you ping the CP/M Host while he is pinging by itself then
you can "see" the Z80 hard working, the answer times goes up to 120 ms
with spikes up to 400 ms


OK - I think enough information, I must continue my work in the next
time, I answer to all questions here ore per email but writing
comments consumes too much time in the moment.

regards Ralf Kästner