File Transfer

[Rich Leary <richar...@gmail.com>]

Eventual addition of a CF or SD card interface to my S-100 system
should make file transfers to or from PC and S-100 (or other systems I
have including Kaypro 10, C-128, N8VEM V1, SBC-2, SBC-3, and some
others I am forgetting) easy. In the meantime I have been
experimenting with alternative connection methods. I thought you might
find some of those efforts and results interesting.

a. I tried using the NetBurner SBL2e X Serial to Ethernet device on my
"modem" port on the S-100 Interfacer 4. On the PC end I used Hyper
Terminal Personal Edition as I was using my Windows 7 laptop. What I
quickly discovered is that the NetBurner is a great device (more on
that later) but that using TCP/IP does not work for XMODEM transfers.
XMODEM demands 100% transparency and a TELNET interface is not 100%
transparent. Since I liked the convenience of the TELNET interface
that allowed me to connect to the S-100 modem port from anywhere in
the house including my desk in the loft where I usually like to
"work". Note: For XMODEM I use MDM727 on the S-100 system with an
overlay based on the easily available overlay for the Interfacer 4.

b. Next I worked on impementing ZMODEM capability on my Kaypro 10.
ZMODEM was targeted because it is stated to work over connections like
TCP/IP (TELNET) and is faster than XMODEM. I used ZMP15 and the
readily available overlay for the Kaypro, ZMO-KP12. I initially just
wanted to get ZMODEM working and was able to do that with a direct
connection at 9600 bps. Once I had that working I switched to the
S-100 environment.

c. I built an overlay for ZMP15 for the Interfacer 4 that was limited
in capability - most notably it had no re-configuration capability. I
initially set the Interfacer 4 to 9600 bps and tried a direct
connection. It did not work. Next attempt backed off to 4800 bps and
that worked. It turns out that in the ZMP15 documentation the author
notes that ZMP15 is unlikely to work above 4800 bps due to the design
of one area that times out after a 100 ms timing loop. While I might
try to tackle that design limitation in the future, at this point I
decided to switch environments. Note: Why ZMP15 worked with the Kaypro
at 9600 must have just been due to minor timing differences in the
read or write rotines. The Kaypro is actually a slower CPU (4 vs 6
MHz) and like the Interfacer 4 does not use interrupts.

d. I moved the NetBurner from the "modem" port to my terminal port
that is normally connected to a Wyse-50 terminal. I then used Hyper
Access on the PC end because it has a nice Wyse-50 emulation. I left
that terminal port speed at 9600 bps. This combination works like a
champ. So my S-100 terminal is now two floors away from the S-100
system and the view towards the mountains is much better. :-)

e. This left me without a remote connection to the "modem" port for
transfers so I tried a bit different set of hardware. I used a pair of
Parani SD1000 Serial to Bluetooth devices. One is connected to the
"modem" port on the Interfacer 4 and the other is connected to a
serial port on the PC. So one Hyper Access window is the terminal for
the S-100 systems and another window is the "remote" system. I tried
ZMODEM across this interface and it worked well although was limited
by the ZMP15 4800 bps limitation. I also reset the SD1000s to 19200
bps and confirmend that they work with XMODEM (again using MDM727 on
the S-100) just fine with no issues seen due to transparency
imitations. Speed is so-so as one would expect in XMODEM at 620-720
bytes per second. ZMODEM would be faster.

So...

1. I recommend both the NetBurner SBL2e X and the Parani SD1000
devices as ways to "break the wires" connecting S-100 or other systems
to terminas, other computers, etc.

2. If anyone has a ZMODEM-capable package that will work at 9600 or
19200 (upper limit of Interfacer 4) I would love to get a copy.

Rich