10 Hostmode
135
Chapter 10
10
Hostmode
The hostmode was developed from
WA8DED
in 1986 in as an alternative firmware for
TARP-TNC’s to enhance the communication between computer (the host) and the
connected TNC.
In the terminal mode the TNC is allowed to transfer data at any time to the computer, but
in the hostmode the TNC is only allowed to send data if being polled by the computer.
This has the advantage that the computer definitely knows when the TNC sends data, i.e.,
the computer controls the data transfer between computer and TNC. This ensures that the
data of each channel will be displayed in the correct window of the hostmode program.
Because of this complete control of data exchange between computer and TNC and
because of the hostmode structure, a transfer of binary files is possible without problems,
and this on several channels at the same time. Special encoders like UUENCODE,
7PLUS, YAPP are not necessary anymore.
As there was no source code for the
WA8DED
firmware available, some German radio
amateur (from the NORD><LINK) decided to program an own firmware. The ideal was
the WA8DED firmware inclusive hostmode for best compatibility to existing programs.
So the NORD><LINK-
TheFimware
was created, short form
TF
. Already from the
beginning the source code of
TheFirmware
was available for anyone, so that radio
amateurs could modify and improve it. Especially for new ideas like extended hostmode
and AX.25 protocol expansions like as DAMA
TheFirmware
was and is the
basis for
development
.
Because of these advantages, the wide distribution of
TF
and the always more perfected
hostmode programs, the hostmode became the standard for TNC controlling.
But the disadvantages of the hostmode shall be mentioned too. The hostmode progam has
to poll the TNC continuously, if data is available or not. That means the program has to
poll in a turn each channel after the other for data. This causes a delay until the data
becomes displayed on the monitor. But the polling is reduced using the extended
hostmode (refer to chapter
). Another disadvantage is the high
load
at the
serial interface caused by multiple transfers of data, i.e., if the monitor is switched on the
receive-data are transmitted once on the monitor channel and once on the receiving
channel to the computer. This disadvantage is visible especially when using high speed
packet (9k6 or higher).
10.1
The PTC-IIIusb hostmode
The hostmode implemented in the PTC-IIIusb is largely compatible to the WA8DED
hostmode, as found in virtually all TNC´s, but is only used when the PTC-IIIusb is
connected to a computer, and controlled by a special hostmode program (e.g.
GP
,
SP
,
WinGT
,
WinPR
,
TNT
, etc.).
After starting the
WA8DED
hostmode the PTC-IIIusb displays in the monitor channel a
short startup message with version number of the firmware and the PTC-IIIusb BIOS.
Additionally all installed modems and the baud rates being set are displayed: