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LU9DCE > PACKET 28.12.16 15:44l 153 Lines 7722 Bytes #999 (0) @ WW
BID : 16176_LU9DCE
Read: GUEST
Subj: PACKET RADIO - PART 14
Path: IW8PGT<CX2SA<LU9DCE
Sent: 161228/1334Z @:LU9DCE.TOR.BA.ARG.SOAM #:16176 [TORTUGUITAS] $:16176_LU9DC
From: LU9DCE@LU9DCE.TOR.BA.ARG.SOAM
To : PACKET@WW
INTRODUCTION TO PACKET RADIO - PART 14
by Larry Kenney, WB9LOZ
TNC COMMANDS - PART 3 OF 3
....continued from part 13
MAXFRAME: Sets the upper limit on the number of unacknowledged
packets the TNC can have outstanding at any time. (The
outstanding packets are those that have been sent but have not
been acknowledged.) MAXFRAME also determines the maximum number of
contiguous packets that can be sent during one transmission. The
value can be set from 1 to 7. The best value to use depends on the
frequency conditions. The better the conditions are, the higher
the value you can use. If conditions are poor due to frequency
congestion, noise, or other variables, (shown by lots of retries)
MAXFRAME should be reduced to improve throughput. The best value
of MAXFRAME is determined through experimentation. MAXFRAME of 1
should be used for best results on HF packet.
MFILTER: This command allows you to enter up to four ASCII character
codes, 0 - $7F, for the control characters that you want eliminated
from your monitored packets. Codes may be entered in either Hex or
Decimal. Here are the ASCII codes for some of the more troublesome
control characters found in monitored packets:
HEX DEC FUNCTION POSSIBLE RESULT $07 07 Control G
Rings your bell or "beeps" your speaker $0C 12 Control L
Form feed - could clear your screen $13 19 Control S Can
cause your screen to stop scrolling $1A 26 Control Z Can
clear your screen $1B 27 Escape Can cause your cursor
to move to a random
point on your screen and can raise havoc
with printer control.
AEA has added a new code, $80, that will not allow ANY control
characters to be displayed on the user's screen from monitored
packets.
MHEARD: An immediate command that causes the TNC to display a list
of stations that have been heard since the command MHCLEAR was given
or the TNC was powered on. This command is useful for determining
what stations can be worked from your QTH. Stations that are heard
through digipeaters are marked with an * on most TNCs. On the AEA
PK-232, the stations heard direct are marked with the *. (Check your
TNC manual.) The maximum number of stations in the list is 18. If
more stations are heard, earlier entries are discarded. Logging of
stations heard is disabled when the PASSALL command is ON. (See
below.) If the DAYTIME command has been used to set the date and
time, entries in the MHEARD list will show the date and time the
stations were heard.
PASSALL: Causes the TNC to display packets that have invalid
checksums. The error-checking is disabled. If PASSALL is ON, packets
are accepted for display, despite checksum errors, if they consist
of an even multiple of eight bits and are up to 330 bytes. The TNC
attempts to decode the address field and display the callsigns in
standard format, followed by the text of the packet. PASSALL can
be useful for testing marginal paths or for operation under unusual
conditions. PASSALL is normally turned OFF.
PERSIST: Used in conjunction with the SLOTTIME command (see below)
to provide less clutter on a busy packet frequency. As more and more
TNCs are upgraded to include the PERSIST and SLOTTIME commands,
fewer and fewer packet collisions will occur. If you have these
commands available in your TNC, you should set DWAIT to 0 and set
these commands for use. Note: On some TNCs, such as the PK-232,
you have another command that determines whether you use DWAIT or
PERSIST/SLOTTIME. It's the PPERSIST command (with 2 P's). Set it
ON to use PERSIST/SLOTTIME; set it OFF to use DWAIT. I strongly
recommend that you set PPERSIST to ON.
PERSIST specifies a threshold value for a random-number attempt to
transmit. The value ranges from 0 to 255. 0 signifies a 1/256th
chance of transmitting every SLOTTIME; 255 allows the TNC to key
the transmitter every SLOTTIME. Through experimentation, it has been
determined that the best value for PERSIST is in the 60 to 70 range.
SLOTTIME: This command determines the time interval the TNC waits
between generating random numbers to see if it can transmit. This
random number generation and the value of PERSIST work together to
provide smoother operation on a busy packet frequency. The SLOTTIME
value may be set from 0 to 250. Through experimentation it has been
determined that the best value for SLOTTIME is in the range of 10
to 20.
SCREENLN n: This parameter determines the length of a line of text
on your computer screen. The value may be 0 to 255, and is usually
set to 40 or 80 depending on the screen display you have. A carriage
return and line feed <CR/LF> are sent to the terminal in Command
and Converse modes when n characters have been displayed. A value
of zero inhibits this action. If your computer automatically formats
output lines, this feature should be disabled.
TRANS: This is an immediate command causing the TNC to change from
Command mode to Transparent Mode. Transparent mode is used when you
want to send data such as executable programs where characters in
the data would conflict with the operation of the TNC. Characters
such as "Control C", "Control R", "Control S", "carriage return",
"linefeed", etc. all effect the operation of the TNC when in
Converse Mode. In Transparent Mode none of the data characters
affect the operation. All eight bits of each character are sent
to the radio exactly as they are received by the TNC from the
computer or keyboard. Packets are transmitted at regular intervals
set by the PACTIME command or whenever a full packet of information
is ready. The receiving TNC must also be in Transparent mode and
nodes and digipeaters cannot be used in the transmit path. Since
the characters normally used for TNC operation have no affect in
this mode, a special procedure is required to exit Transparent
Mode and return to Command Mode. Refer to your TNC operating manual
for details on how this procedure is performed on your particular
TNC. You should also check your manual for information on the
CMDTIME, PACTIME, START, STOP, TRFLOW, TXFLOW, XFLOW, XOFF and XON
commands before using Transparent Mode.
TXDELAY n: This parameter tells the TNC how long to wait before
sending data after it has keyed the transmitter. All transmitters
need some start up time to put a signal on the air. Some need more,
some need less. Synthesized radios and radios with mechanical
relays need more time, while crystal controlled radios and radios
with diode switching require less time. External amplifiers usually
require additional delay. Experiment to determine the best value for
your particular radio. TXDELAY can also be useful to compensate for
slow AGC recovery or squelch release times at the distant station.
There are many additional commands available to you. Spend some
time reading the owner's operating manual that came with your TNC
to discover some of the surprises the other commands offer. New
versions of the TNC software have added several commands that you
might find useful in your packet operating.
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