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1993-05-06
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From DB2OS to TNC2 @WW
TS: BF - Date/time: 0218/1121 - BID: 182308DB0FAU
Title : TheFirmware TF24c Update Information
Path: !LX0PAC!DB0GE!DK0MTV!DB0GV!DB0SIF!DB0EAM!DB0FAU!
de DB2OS @ DB0FAU
NORD><LINK's THE FIRMWARE
AX.25 Version 2
Multi Channel TNC Firmware
Version 2.4c
1. Introduction
The Firmware Version 2.4c DAMA/SMACK (xx Channel)
Copyright by NORD><LINK, xx-xx-xx
Free for non-commercial usage
Checksum (xxxx) = xxxx
This is the message that the new version of The Firmware should display
in Terminal Mode when booting.
The Firmware can be installed in any TNC-2 (or compatible TNC).
This document is all about the latest official version of The Firmware
from NORD><LINK. The software no longer mentions all the contributing
authors when booting since there are many that have worked together on
developing the software over the years.
The original author of The Firmware was Michael (DC4OX). The DAMA
implementation was developed by Frank, DL8ZAW. Various improvements have
been contributed by DF2AU, DB2OS, DK6PX, DL9HCJ, DL1MEN, DF7ZE, and
others (See Below).
This version (2.4c) is hopefully free of bugs. However, it has always
been the intention to continually improve the software and to fix known
problems as soon as possible.
2. What Does "The Firmware" Support ?
This firmware supports fully the AX.25 Link Layer Protocol, Version 2 as
specified in October 1984 by the ARRL. The old version of the protocol
(1.x) is virtually extinct and as such, The Firmware no longer supports
it.
The software can support multiple, simultaneous QSO's, each on a
separate logical channel (or stream, as it is sometimes called). The
number of channels supported by each EPROM is determined at compilation
time. The usual configuration has 10 channels available, but versions
with upto a maximum of 27 channels can be built for use by mailboxes
etc.
This version also supports user-access of TheNetNode nodes running the
DAMA protocol. DAMA is an extension of the AX.25 protocol and provides
users with many advantages and improvements over normal AX.25.
The Firmware will automatically determine whether to use DAMA or normal
AX.25 when connecting to a station. Frames received from a DAMA Master
are always displayed with "[DAMA]" appearing after the received text.
The TNC will then only transmit when instructed to do so by the Master.
Channels connected to non-DAMA equipped stations will be unaffected and
transmit in the normal manner.
If the TNC does not receive a "Poll" frame from the "Master" within a
user definable interval, it will switch out of DAMA mode.
When the TNC is operating as a DAMA Slave (that is, a user) and it
receives a frame to be digipeated, it does so immediately.
The DAMA Protocol is described in CQDL, the magazine of the German
national society, in the April 1989 issue. It is also described in the
paper, "DAMA - A new method of handling packets ?" by Detlef Schmidt
(DK4EG) in the Proceedings of the 8th ARRL Computer Networking
Conference, October 1989 (ISBN 0-87259-251-0).
2.1. KISS and SMACK
The new KISS compatible protocol "SMACK", developed by DL5UE and DK5SG,
is also supported by this release of The Firmware. See the release
documentation for details about SMACK.
The user defined Hostmode parameters are remembered when either normal
or SMACK KISS modes are in use. They are also retained following a
reset. Switching out of KISS/SMACK mode back to Terminal mode restores
the values stored previously.
The SMACK/KISS $FF frame carries the usual meaning and is used to switch
out of that mode and back into normal The Firmware "Terminal" mode.
It should be noted that the internal software clock does not continue to
keep real time whilst either KISS or SMACK is in use.
2.2. Startup and the EPROM Checksum
Following each reset, the EPROM checksum is recalculated. This must
agree with the checksum shown in the round brackets of the startup
message. If the two do not agree, then it is likely that the EPROM has
been programmed incorrectly or that the code programmed was corrupted in
some way.
After first installing the EPROM, it is useful to perform a warmstart
using the "<ESC> QRES" command since some TNCs have problems with old
code held in the battery-backed RAM. This will also load the RAM with
the default set of parameters from EPROM.
After the QRES command, the TNC callsign is empty and can be set using
the "<ESC> I" command. Other parameters can be set in a similar manner.
The user defined values are stored in the battery-backed RAM.
3. Basic Operation in Terminal Mode
All commands and information are sent to the TNC as lines of text. Each
line can be upto a maximum of 256 characters in length including the
delimiting Carriage Return (<CR>). If the 256th character is not an
<CR>, it is ignored and a "Bell" (<BEL>) is sent to the Terminal.
Single characters can be erased using either Backspace (<BS> = Hex 08)
or Delete (<DEL> = Hex 7F).
Control-U and Control-X will delete a whole line.
Control-R will move the cursor to the first character of the current
line. A second Control-R moves the cursor back to the end of the line
ready for more input. Between these two Control-R's, all other input
except for <XON> and <XOFF>, is ignored.
Bell (<BEL>) characters are sent direct to the terminal.
Lines beginning with the Escape (<ESC>) character cause a asterisk "*"
to be displayed thus denoting that this is the start of a command line.
Commands sent without parameters will display the current value of that
parameter.
Lines beginning without <ESC> are taken as being Information and are
sent out on air.
4. General Terminal Mode Information
The Logical Channels
The Firmware in its standard form provides 11 logical TNC channels to
the user. The terminal is always logically connected to one of these
channels which is selected by the "<ESC> S" command.
Channel 0 is reserved for sending only UNPROTO information eg CQs, IDs
and BEACONs. The path to be used for this channel is, like the others,
set using the "<ESC> C" command.
The other 1-10 channels can also send in UNPROTO mode, as long as they
are not connected to another station. Connect requests can be mode on
any free channel. Incoming connect requests from other stations are
given the next free channel in sequence providing that the maximum
number of simultaneous connects (set using the "<ESC> Y" command) has
not been exceeded.
4.1. Selecting Channels
Information arriving on a channel that is not currently selected, is
stored in RAM until that channel is chosen for display using the "<ESC>
S" command.
The "<ESC> L" command, without parameters, can be used to ascertain the
connect status of each channel and whether there is data waiting to be
read. If any one of the unselected channels has data waiting to be read,
this is also shown by the STA LED of the TNC lighting up.
Even if a station disconnects, data is kept in RAM. This makes it
possible to store messages when the TNC is unattended. In short, a very
simple mailbox!
4.2. Changing the Connect Path
There is no need to disconnect a station before trying over a different
path. Just use the "<ESC> C" command to enter the new path for the
desired channel and a reconnect attempt will automatically be made using
the path entered. No data is lost during this process.
It is not possible to connect to the same callsign on two different
channels. This is a restriction of the AX.25 protocol.
4.3. The AX.25 Protocol
The Firmware always uses version 2 of the AX.25 protocol. Connect
requests made using version 1 of the protocol will be immediately
disconnected. Version 2 is better on busy networks.
The Firmware also "polls" in version 2 of AX.25. As soon as there is no
more information to send, a timer is started. If this timer runs for
more than 3 minutes, a poll frame is sent to the other TNC thus ensuring
that the link is still in use.
The number of "retries" attempted for any frame is set by the "<ESC> N"
command.
4.4. Commands for Individual Channels
The commands, <ESC> F, I, N, O, and V can be set independently on each
selected channel. Channel 0 holds the default value of each of those
parameters.
A channel is selected, any of the parameters above set for just that
channel and a connect is made. The QSO then proceeds using those values.
As soon as the QSO ends, the values are reset to those held in the
Channel 0 defaults.
5. The Firmware's Monitor Functions
The "<ESC> M" command is used to activate the channel traffic monitor.
The parameters given to this command determine the types of frames that
are seen in the monitor output. More than one parameter can be given in
the same command line.
Parameter Packet-Type
--------- -----------
N Monitor OFF
I Show Information Frames
U Show UNPROTO Frames
S Show Supervisory (control) Frames
C Monitor whilst connected on selected channel
+ Only Packets from/to given Stations (max 8)
- Show no packets from/to given Stations (max 8)
For example;
<ESC> M N - Switch the monitor off
<ESC> M IUS - Show Info, Unproto and Supervisory packets
<ESC> M + G6DHU - Show only packets to/from G6DHU
<ESC> M - G6DHU - Don't show G6DHU's packets
The "+" and "-" parameters may not be used in the same command line and
they must appear as the last parameter before the callsign. A parameter
of just "+" or "-" will erase the current list of calls to be
monitored/ignored.
5.1. Monitor Output Format
The station digipeating a packet is shown with an asterisk "*".
AX.25 Frame types as they appear in monitor output are as follows;
Name Meaning
---- -------
RRa Ready to Receive (frame acknowledge)
RNRa Receiver Not Ready (temporarily busy)
REJa Reject or duplicate packet
UI UNPROTO information (broadcast)
DM Busy
SABM Connect Request
DISC Disconnect Request
UA Acknowledge Unnumbered frame
FRMR Frame Reject (Protocol Failure)
Iab Information
?ccH Undefined or Unknown frame
Where;
a = Sequence Number of the next expected frame
b = Sequence number of this packet
cc = Hexadecimal number
A final character denotes the status of the Poll/Final and
Command/Response bits of the AX.25 protocol;
<none> = Protocol version 1 without P/F Bit
! = Poll/Final Bit in Protocol version 1
^ = Command Packet in Protocol version 2 (no Poll Bit)
+ = Command Packet in Protocol version 2 (with Poll Bit)
- = Response Packet in Protocol version 2 (with Final Bit)
v = Response Packet in Protocol version 2 (no Final Bit)
The Protocol Identifier (PID) byte is shown in Hexadecimal.
Note: The monitor will only function when there are more than 256 free
buffers available in the TNC.
6. More General Terminal Mode Commands
6.1. Connect Text
The "<ESC> U" command allows a connect text to be set and switched on
and off. This allows you to set a small welcoming message perhaps
inviting a caller to leave a message. The connect text message is sent
automatically to any connecting station and in no way affects operation
by the user.
When Connect Text is enabled, any incoming text and status messages for
other channels are saved in RAM until that channel is selected. Status
messages and data received can thus be seen in the correct chronological
order.
In the event of a channel containing much saved data, remember that the
"<ESC> Z" command can be used to select XON/XOFF flow control. When
enabled, this allows Control-S to stop the output from the TNC and
Control-Q to resume it. Messages can then be read without loss of
important data.
6.2. The Heard List
The internal "Heard" List is activiated by the "<ESC> H" command. The
heard list implemented by The Firmware is somewhat different to that
found in other TNC software in a number of ways.
Firstly, it is not a list of the "last 20 stations heard" kind. That
sort of list doesn't have much use in today's busy channels. The
Firmware implements a dynamic heardlist. The number of calls stored is
determined by the free buffer space available in the TNC RAM. With the
standard 32k TNC RAM, it is possible to store upto 600 calls. The growth
of the heard list can be limited by a user definable parameter.
For each station heard, the list saves;
- Callsign and SSID
- Date and Time first heard
- Date and Time last heard
- Number of I-Frames heard
- Number of RR-Frames heard
- Number of REJ-Frames heard
- Number of RNR-Frames heard
The digipeater path is no longer saved since with today's node network,
this not often of use.
The Heard List can provide useful information about the quality of the
local channel and of the links between its users. For example, a station
with a high I-frame count and low RR and REJ counts denotes a good link
quality.
There is a small performance overhead in maintaining the heard list
which obviously increases with the size of the list. The list update
mechanism can be switched off with the command "<ESC> H 0". The list
remains in memory whilst switched off but incoming packets are no longer
searched for inclusion in the list.
6.3. The Heard List in Hostmode
The H command also works well in Hostmode. When requesting the heard
list it is important to remember the following points.
The first line (H, Number stations heard, maximum number in list) is
sent with Hostmode Code 1 (Success, Message follows null terminated).
The actual heard list is then sent G/G0 to Channel 0 in Hostmode Code 5
"Monitor Header" format (Monitor Header, null terminated, Info follows).
The last line of the list is sent with Hostmode Code 4 (Monitor header,
null terminated).
The heard list is memory resident, that is, it is saved following a
reset or switch off and is held in the battery backed RAM.
6.4. The Real Time Clock
Version 2.4c of The Firmware also has a built-in 24 hour clock and
calendar. It is possible to timestamp all status messages (eg CONNECT
REQUEST from, CONNECTED to etc) aswell as the header of each monitored
packet.
The "<ESC> K 0" command switches off any timestamping. "<ESC> K 1"
switches on timestamping of TNC status messages and "<ESC> K 2" switches
on timestamping of both TNC status messages and monitor headers.
The "<ESC> K" command displays the current Date and Time and depending
on how the time and date information was entered, it can be displayed in
either American or European format. Date and time are reset to 00/00/00,
00:00:00 after a cold or "<ESC> QRES" restart. After a warm start, the
clock continues to run from the previous value stored when the TNC was
switched off.
7. Software Improvements
This section summarises the major changes in this version of the
firmware.
7.1. AX.25 T1 (Acknowledgement Timer) or FRACK
There is no longer a fixed value for the ACK timer. The firmware now
measures in real time, the interval between sending a frame and
receiving its acknowledgement. This value is then smoothed and used to
continuously vary the T1 timer value according to the prevailing channel
conditions.
The time measured, or RTT (Round Trip Time) is smoothed from wide
variations through the formulae;
- with rising RTT: SRTT' = ( a1 x SRTT + RTT ) / ( a1 + 1 )
- with falling RTT: SRTT' = ( a2 x SRTT + RTT ) / ( a2 + 1 )
Therefore, the SRTT (Smoothed Round Trip Time) contains a time averaged
history of previous RTTs. The parameters a1 and a2 are settable by the
user and default to 7 and 15 respectively.
The relationship between the AX.25 T1 timer and the SRTT is;
T1 = a3 x SRTT
where the a3 parameter is user settable (Default = 2)
The SRTT must be initialised to a value before the QSO commences, as at
that time, the SRTT cannot be known. This initial value of SRTT can be
set using the "<ESC> F" command which accepts a parameter, the initial
SRTT in 10ms increments (Default = 700). The RTT measurement process is
started after the connection is acknowledged ie after the UA frame is
sent by the station to be connected to. When the connect path involves
digipeaters, the RTT is increased due to the expected extra delay by;
T1 = (2 x "Number of Digis" + 1) x IRTT
A1, a2 and a3 can be set with the "<ESC> @A1", "<ESC> @A2" and "<ESC>
@A3" commands. These parameters are especially important when using a
FlexNet node which holds back the UA (acknowledgment) frame following a
connect request, until all nodes along the path have responded to the
request. As soon as the connect request is acknowledged, the RTT
measurement is started.
7.2. DWAIT from DL4YBG
Before each information frame is sent out, the TNC will wait for one
Slottime interval before the P-Persistence algorithm is started. This
holds irrespective of whether the TNC is operating in SMACK, normal KISS
or non-DAMA The Firmware modes.
When operating as a DAMA Slave, the persistence parameters are
automatically set to Slottime = 0 and Persistence = 255 allowing the TNC
to respond immediately after being asked to send data by the Master.
The chance of packet collisions is reduced by implementing this
strategy.
7.3. I-Frame Polling from DK6PX
When sending small frames, that are subsequently missed by the receiving
TNC, it is sensible to resend the unacknowledged I-frame with the Poll
bit set instead of sending an RR frame.
The "<ESC> @I" command can be used to set the threshold packet length at
which this strategy reverts to normal polling action. "<ESC> @I 0" will
force normal polling to be used at all times, which is also the default
when the TNC is operating in DAMA mode.
7.4. Dynamic MAXFRAME from DK6PX
According to packet length, MAXFRAME is automatically increased when,
for example, other pending packets are of small size.
With MAXFRAME set to 1, a maximum of one frame with 256 characters is
sent. If there are two frames pending with length 128, MAXFRAME is set
to 2. The default initial value of MAXFRAME is 4.
7.5. DCD/PTT Lock-up
A previous bug in one of the software interrupt routines, could under
certain circumstances cause TNC lock-up. This bug existed in all
previous versions of The Firmware and was solved by Y51GE. Another
related bug which caused DCD lockup was also fixed.
7.6. DAMA Parameters
When DAMA mode is deactivated, the parameters P, W, B and @T2 are
automatically reset to their user defined values.
7.7. Disconnect from DL1MEN
If a pending connect request is aborted with the "<ESC> D" command, a
DISC (Disconnect) frame is automatically sent. This prevents the station
that was to have been connected with, from sending any unnecessary
frames following the connect abort.
7.8. Heard List
The heard list now shows the last heard station rather than the first
heard station. If the heard list is full, the oldest call is removed.
8. The Firmware Command List
8.1. ESC A [0|1]
Send Linefeed (<LF>) character to terminal after each Carriage Return
(<CR>). (1 = Yes, 0 = No, Default = Yes)
8.2. ESC B [<n>]
Time interval in seconds after which DAMA mode is deactivated when no
Poll frame from the DAMA Master is received.
"<ESC> B 0" = Switch off DAMA mode completely
"<ESC> B" displays "Interval (Actual Value)" eg "120 (93)"
Default = 120 seconds.
8.3. ESC C [Call] [Digi List]
Make a connect to the given call. Note that the keyword "v" or "via" is
*not* required between the Call and the Digi List.
"<ESC> C [Call]" on Channel 0 sets the callsign (and optional path) to
be used for UI-frames. For example set;
ESC C ID
or
ESC C CQ
8.4. ESC D
Disconnect the currently selected channel.
If there is still data to send or to be acknowledged, the QSO will
continue until so done. If this is not what is required, a second "<ESC>
D" command can be given to abort the connection.
If the currently selected channel is already in the disconnected state,
all channel settable parameters are reloaded with their defaults held in
Channel 0.
8.5. ESC E [0|1]
Echo all characters sent to the TNC.
1 = Yes, 0 = No, Default= Yes.
8.6. ESC F [<n>]
Set initial the FRACK value which determines how long to wait for an
acknowledgement after an I-frame is sent. This interval can be input in
seconds. If the parameter input is less than 16, the value is multiplied
by 100 and divided by the A3 parameter (input via "<ESC> @A3"). Input
parameters greater than 15 are taken as milliseconds (ie the Level 2
Round Trip Time).
Default = 250
8.7. ESC G [0|1]
This is a hostmode only command and is used to inquire as to the status
of the current channel.
If entered in Terminal mode, an error message will be given.
8.8. ESC H [<n>]
Display the heard list and set the heard list parameters.
Examples;
H - Display Heardlist
H 0 - Heardlist Update Off
H 1 - Heardlist Update On
H 2 - Clear Heardlist
H n - Maximum Number of calls in list (n > 2)
The list is shown in order of the last callsign heard and the oldest
heard callsign will be overwritten when the list becomes full.
The heard list is resident. It remains saved in the battery backed RAM.
Default = 0 (Heardlist off)
8.9. ESC I [Call]
Set MYCALL for the TNC. After a cold-start, the call is unset.
The callsign can be set independently on each channel and when that
channel is disconnected, the call set in Channel 0 is again assumed for
that channel.
Note that the TNC will only transmit *after* the call has been set using
this command.
8.10. ESC JHOST[0|1]
This command is used to toggle between Hostmode and Terminal Mode. Host
mode is not a "human" interface and is designed for computer control.
Packet terminal programs such as GIPSY, THP, AHP, SP (Super Packet) and
Packet Master use this Host mode interface.
8.11. ESC K [<n>]
Activate timestamping of status messages and monitor headers. The built
in real-time clock/calendar is used.
Examples:
K - Display current Date and Time
K 0 - Timestamping OFF
K 1 - Status Message Timestamping ON
K 2 - Status Message and Monitor Timestamping ON
K 20.02.88 - Set Date - European format
K 02/20/88 - Set Date - American format
K 17:36:00 - Set Clock time
Default = 0 (All timestamping OFF)
8.12. ESC L [0..10]
This command is used to display the status of logical TNC channels. If
given without parameters, the status of all channels will be displayed.
Information such as connect path, frames received, frames to be sent,
frames to be acknowledged and retry counter value are displayed.
The currently selected (ie default) channel is displayed with a "+"
mark.
8.13. ESC M [IUSCN+-]
This command is used to select the monitor mode. The parameters to the
command determine the types of frames displayed by the monitor and also
which stations are selected or filtered from the display.
Examples:
N None (Monitor OFF)
I Show only Information Frames
U Show only UI frames (CQ, BEACON etc)
S Show Supervisory frames
C Monitor whilst connected
+ Followed by list of upto 8 calls
which will be the only ones shown.
- Followed by list of upto 8 calls
which will be ignored.
The "I", "U", "S" and "C" parameters may be combined in a single
command. For example, "<ESC> M IUSC" will display all possible frame
types and the monitor will be active when a channel is in the connected
state.
The "+" and "-" parameters may *not* be combined in a single command.
The command with just a "+" or "-" parameter will clear the lists and
return to normal operation.
Default = UI (Monitor displays UI and Information frames)
8.14. ESC N [0..127]
Set the maximum number of retries for each Information frame sent. A
value of 0 instructs the TNC to retry forever.
The retry counter can be set independently on each channel. When that
channel is disconnected or a RESET command is given, the retry value
stored in Channel 0 becomes the default.
Default = 10 (Tries)
8.15. ESC O [1..7]
Set the maximum number of information frames that may be outstanding and
unacknowledged at any one time (MAXFRAME).
The MAXFRAME can be set independently on each channel. When that channel
is disconnected or a RESET command is given, the value stored in Channel
0 becomes the default.
Default = 2 (Frames unacknowledged)
8.16. ESC P [0..255]
Set the TNC's Persistence value for determining channel access priority.
DAMA Slaves always set P = 255.
Default = 32 (32/255 chance of access)
8.17. ESC QRES
Cold start The Firmware and reload the EPROM defaults.
8.18. ESC R [0|1]
Enable the TNC digipeat function. 1 = Yes, 2 = No.
Default = 1 (Allow TNC to digipeat)
8.19. ESC S [0..10]
Select the given logical channel. 0 is the Monitor channel.
Default = 0 (Default channel is the monitor channel).
8.20. ESC T [0..127]
Set the delay between keying the transmitter and sending a data
(TXDELAY). The value given is in 10ms increments. For example, a delay
of 300ms would be "<ESC> T 30". The value should be experimented with to
suit your TX, but set it as low as possible.
Default = 25 (250ms)
8.21. ESC U [0|1]
Set (or display) the Connect Text for the TNC. The text is saved even if
the function is switched off.
Examples:
U 1 "Hello!" Enter Connect Text
U 1 Enable Connect Text
U 0 Disable Connect Text
U Display Connect Text
Default = 0 (No Connect Text, Disable Connect Text).
8.22. ESC V
Display the current AX.25 Protocol Version in use. Protocol version 1 is
no longer supported by The Firmware from v2.4 onwards.
8.23. ESC W [0..127]
Set (or display) the TNC Slot Time to be used in determining channel
access priority. The value given is in milliseconds.
Default = 10 (ms)
8.24. ESC X [0|1]
Disable the transmitter PTT line.
Default = 1 (PTT enabled)
8.25. ESC Y [0..10]
Set (or display) the maximum number of simultaneous connects allowed to
or from the TNC. If given without parameters, the command will display
"Max No. Connects (Occupied Channels)". This is only the case when all
channels have the same SSID set as that on Channel 0.
Example: "4 (1)"
Default = 4 (A maximum of 4 channels in use at any one time).
8.26. ESC Z [0..3]
Determine TNC flow control and XON/XOFF handshaking.
If flow control is enabled, the TNC will not send data to the terminal
if a command or data to be sent is being entered. When flow control is
disabled, the TNC will immediately send any data to the terminal
regardless of whether a command or data is being entered.
If XON/XOFF handshaking is enabled, the user may stop TNC output with
the Control-S key and restart it with Control-Q.
Examples:
0 Flow On , XON/XOFF Off
1 Flow Off , XON/XOFF Off
2 Flow On , XON/XOFF On
3 Flow Off , XON/XOFF On
Default = 3 (Flow control off, XON/XOFF on)
9. Extended TNC Commands
There are a number of extended TNC commands that are prefixed with the
"@" character eg "<ESC> @A1".
9.1. ESC @A1 [<n>]
Set or display the a1 SRTT calculation parameter. Default = 7.
9.2. ESC @A2 [<n>]
Set or display the a2 SRTT calculation parameter. Default = 15.
9.3. ESC @A3 [<n>]
Set or display the a3 SRTT calculation parameter. Default = 3.
9.4. ESC @B
Display the free buffer count in the software.
9.5. ESC @D [0|1]
Enable Full-duplex mode. Default = 0 (simplex)
9.6. ESC @I [<n>]
Set (or display) the I-poll threshold. The value given is the number of
bytes at which if packets longer than that are waiting to be sent, I-
poll will not be used.
Default = 60 (bytes)
9.7. ESC @K
Start KISS/SMACK mode.
9.8. ESC @M [0|1]
Set 7 or 8 bit (binary) terminal mode.
When in 7 bit mode, control characters are automatically displayed with
a leading "^" prefix. In 8 bit or binary mode, control characters are
passed through without translation.
Note that XON/XOFF should not be used at the Terminal end as it may hang
when seeing the XOFF ("^S") character.
The default is to operate in binary mode (@M = 1) and the character
translation does not occur. The command is however important when using
Hostmode software eg THP, SP etc.
0 = 7-Bit; 1 = 8-Bit (only in Terminal-Mode)
Default = 1 (binary, 8 bit mode)
9.9. ESC @T2 [<n>]
Time interval to delay acknowledgement of received frames.
Default = 150 (1.5 seconds)
9.10. ESC @T3 [<n>]
Set or display the link "keep alive" timer. If the link has been
inactive for @T3 seconds, the link partner is polled for activity.
Default = 18000 (ms)
9.11. ESC @V [0|1]
Enable callsign checking, eg rejection of connect requests from
"NOCALL". (1 = Enabled, 0 = Disabled).
Default = 0 (disabled)
10. Acknowledgements
Original documentation in German by DB2OS, DF2AU und DC4OX.
Updated by DJ1OR September 1992.
English translation by Mike Chace (G6DHU) February 1993.
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