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EI2GYB > PACKET 04.12.18 11:45l 122 Lines 7141 Bytes #999 (0) @ WW
BID : 3218_EI2GYB
Read: GUEST
Subj: INTRODUCTION TO PACKET - Part 14
Path: IW8PGT<CX2SA<SV1CMG<PI8BDG<AB0AF<KE0GB<GB7YEW<ZL2BAU<EI2GYB
Sent: 181204/0936Z 3218@EI2GYB.DGL.IRL.EURO BPQ6.0.16
INTRODUCTION TO PACKET - Part 14 - by Larry Kenney, WB9LOZ
TNC COMMANDS - 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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