NadaNet is a native Apple II network using the built-in serial inputs and outputs
of the Apple II main board. In particular, it uses the Annunciator 1 output and
the Pushbutton 1 input. Logically, the input and output are connected together,
then all the combined "input-outputs" on all networked machines are connected together.
(Electrically, it is only slightly more complicated than that.)
This connection allows each machine to both read the state of the network bus and
cause it to be at a high logic level (1). When no machine is driving it high, the
bus is passively pulled to the low logic state (0). Thus, the network behaves as a
wide OR-gate.
Since all machines are able to control the bus individually under software control, it
is possible to write programs which allow all connected machines to make orderly use
of the network to communicate with all other connected machines. Accomplishing this
requires that the software enforce a discipline for gaining control of the network and
sending data, and that complementary software controls the receiving machines to ensure
reliable data reception.
The Oscilloscope trace below is a display of the network
performing a protocol involving a request message and a response message. The two 8-byte
messages take slightly less than 2 milliseconds (the horizontal axis is 0.2 milliseconds
per division and the vertical axis is 2 volts per division).
NadaNet Capabilities
You might wonder what such a simple network is capable of doing. First, its data rate
is surprisingly high for an all-software network. It can sustain a data transfer rate of
over 10K bytes per second using 256-byte packets, with all synchronization and protocol included. Second, it can
support virtually any protocol, although I have so far implemented only a simple set of operations
useful for network and parallel programming.
Finally, in its current implementation, it
supports up to 15 networked machines, though it could be extended easily to twice that number.
Most NadaNet testing has been done with a 10-machine network of enhanced and unenhanced
Apple //e machines.
The current software supports only Apple II machines, and only those that have a 16-pin
game port on the main board (including the IIgs if it is set to "slow" mode in the control panel).
There is, however, one exception of which you should be aware. Apple decided to "brute force"
a problem they were having with RFI on certain late-model Enhanced //e and Platinum //e machines
by paralleling the pushbutton inputs on these machines with large-value capacitors (0.1uF),
rendering the inputs on these machines useless for fast signaling until the capacitors are "snipped",
as described in the Machine Compatibility section at the end of
this paper.
TCP/IP is not implemented on NadaNet, and I have no plans to do so. Like most other
people, I already have much more suitable computers for connecting to
the Internet, and have no interest in burdening either me
or my Apple II machines with a protocol whose complexity and storage requirements are
larger than all but the very largest 8-bit Apple II applications. I intended NadaNet as
a versatile network environment for learning and parallel programming, for which many
interesting programs would be a few dozen lines of Applesoft BASIC, and doing this in a
TCP/IP environment would be like using an elephant to transport a flea!
NadaNet, complete with its protocols and an ampersand interface for BASIC occupies a
little over 2KB of memory--much less than DOS--and easily co-resides with ProDOS or
DOS while remaining capable of hosting very substantial application programs.
I plan to continue to add tools and application examples to the site. The latest is
a File Server, written in Applesoft, that serves the ProDOS
file system of its host machine to all NadaNet clients, whether or not they are running ProDOS.
Another is CRATE.SYNTH, an 8-voice sampled music synthesizer that
uses NadaNet for initialization and synchronization.
I invite you to look over what is presented, and, if you find it intriguing and would
like to play with it, download the software, build a couple of
little adapters on 16-pin DIP sockets,
and do your own experiments. You'll have a lot of fun getting two or more of
your Apple II computers talking! Of course, I'd be delighted to hear about your ideas
and experiences.
If you'd rather not build the adapters yourself, a small quantity is available for sale
from Bill Garber at $30 per pair, including both
a ProDOS and a DOS 3.3 NadaNet disk.
Version 2.0 of NadaNet is the current version. It is a speed upgrade from the previous
version (which I will refer to as version 1.1, although it was unnumbered). The new
SENDPKT and RVCPKT routines were written by Stephen Thomas, who discovered that the
old RCVPKT was creating a "bus fight" which, although it worked, was putting unnecessary
strain on the electronics of the Apple II. In the process of correcting the fight, we found
ways to increase the transmission speed by 11%, and improve the regularity of packet structure.
As a result, the low-level message format has been altered somewhat, making version 2.0
incompatible with version 1.1 code.
Therefore, you should update all instances of NadaNet on a network if moving from
version 1.1 to version 2.0. At this early stage in NadaNet deployment, this should
not create a problem. All higher level code based on NadaNet is unaffected, except that
performance is improved.
Here are links to ShrinkIt disk images containing the Merlin Pro source files and the object files
and various Applesoft programs using NadaNet.
(Of course, this code must run on a real Apple II--emulators don't cut it. ;-)
![[IMAGE]](NadaNet-logo.gif){kind=logo}
![[IMAGE]](NadaScope.jpg)