Kantronics KPC-4 - Page 41

mn
The WEFAX Command
To
cause
your
TNC
to
enter
the
WEFAX
Mode,
you
use
the
WEFAX
command.
KPC-4
and
KAM
owners
must
remember
to
set
MAXUSERS
to
0/1
before
issuing
the
WEFAX
command.
WEFAX n
This
command
will
cause
the
TNC
to
sample
the
audio
input
at
n
samples
per
second.
The
value
of
n
is
determined
by
the
number
of
pixels
(dots)
which
can
be
displayed
across
one
line
of
your
terminal
screen
in
the
graphics
mode.
For
instance,
if
the
PC computer you use has 640 dots across the screen and the WEFAX station is
transmitting
2
lines
per
second
(120
per
minute)
you
should
use
an
n
value
of
1280.
These
values
keep
your
TNC
in
sync
with
the
HF
WEFAX
transmitting
station.
If
your
WEFAX
picture
skews,
adjust
the
TNC
clock
by
using
the
command
DAYTWEAK.
The
ABAUD
rate
of
the
TNC
must
be
set
and
permed
to
a
value
at
least
5/4
the
WEFAX
n
rate.
This
gives
the
terminal
program
time
to
display
or
store
each
pixel
byte
and
to
handle
the
extra
start
and
stop
bits
added
to
the
8
pixel
bits/byte
(coming
at
xxxx
baud
rate).
XFLOW
may
be
used
with
WEFAX.
To
stop
the
sampling
of
WEFAX
data
and
return to Command Mode, simply send a Ctrl-C to the TNC.
If you are using the Kantronics MAXFAX or PACFILE program with a PC compatible,
you should set the ABAUD to 9600 in the TNC and PERM it at that value.
Suggestions for Writing a WEFAX Terminal Program
Preferences will vary for each WEFAX terminal program writer or user, but the
following functions seem appropriate, at a minimum, for enjoyable operation.
WEFAX Program Functions:
1. Be able to display maps and charts on your computer screen as they are being
received (real time).
2. Be able to store them to disk as they are being received or after you have taken
a look.
3. Be able to print the displayed or stored maps or charts.
4. Be able to clear the screen or map storage area at any time.
What about hardware requirements? First of all, you'll have to have enough computer
storage to handle the resolution you want. To save every pixel the HF station sends,
you'll need up to 1800 lines, each line being your screen width in pixels (PC 640 pixels
or 80 bytes), or 135K bytes! However, your screen will not show this much. A PC or
compatible in graphics mode can display 200 by 640 pixels, so we suggest that you
write your program to save, for instance, 600 of 1800 lines at 640 pixels, or 48K bytes.
Then, you'd be saving every third line received and sampling at an incoming bit rate
of 1280 (640 by 2, hence the reason for WEFAX 1280). This will also improve the aspect
ratio of the saved image, since the pixels on your PC screen are not square, and the
picture is scanned at a resolution of 96 lines per inch. For the standard Macintosh, the
normal screen is 512 pixels wide by 342 pixels high. The screen can therefore display
age = a single picture at one time, but the horizontal resolution is slightly less than
the PC.
WEFAX 33
© Copyright 1989, Kantronics, Inc. All Rights Reserved. a
Duplication of this manual or the firmware without Version 2.85
permission of Kantronics, Inc. is prohibited. Operations Manual