SCS PTC-IIex, Manual

Page: 157 / 220

10 Hostmode
0:
Scan-Stop! Currently the frequency MUST NOT be changed! (After that, if the
modem does not indicate a connection to a user within a few seconds, the %W0
command should be resent to the modem, and so on.)
1: Currently the frequency can be changed, scanning need not to be suspended because
no link establishment is in progress. Response “1” also indicates that the modem
has entered the so-called WAIT state. If the modem is in WAIT state, it does not
accept user calls on the HF port (it cannot be connected by a user) any more.
Now the external scanner can perform a frequency change. After that it must release
the modem from WAIT state by sending %W1 to it. After receiving the %W1
command the modem again accepts user calls on its HF PACTOR port.
%W1
Possible response of the PTC: none.
Release from WAIT state. The modem enters the normal “standby state” again and waits
for incoming user calls.
Note: WAIT state always automatically times out after 10 seconds.
The following chapters are only applicable for software authors! If you do not
want to write your own hostmode program you can skip the following chapters.
10.5 Extended hostmode
The PTC-IIex supports the so called extended hostmode . The extended WA8DED -
Hostmode has established itself as a de-facto standard for communication between
TNC/PTC and PC-control programs.
The extended hostmode makes the polling of the channels much easier and thus reduces
the polling overhead.
In the extended hostmode , channel number 255 is dealed in a special way. A G command
to channel 255 leads to the output of "255,x,y,z,...,0" from the TNC. x, y, x, etc. are the
numbers (binary and increased by one) of the channels that contain new information,
which can be requested with the G command. The string given by the TNC on a poll of
channel 255 always ends with "0".
If, for example, only the monitor channel contains new information, the answer string of
the TNC to a G-poll of channel 255 is 255,01,01,0. If there is no new information to be
received, the output is 255,01,0 (255,0 is also possible). If there is new information in
channel 2 and 3, the string is 255,01,03,04,0. The channel numbers are usually given in
increasing order - at least the PTC-IIex follows this recommendation.
With the extended hostmode , a continuous cyclic polling of every single channel with the
G command has thus become obsolete, just channel 255 needs to be polled regularly. If
the result indicates that there is information in any other channel, only the respective
channel has to be polled using the G command to get the data.
143