Chapter 6 - System Operation and Control
36
the control key and typing a letter C. This character is designated CTRL-C, Some Computers which
do not have a control keys such as the Radio Shack Color Computer, have other methods of enter-
ing such characters. Also, some of the special-function keys (such as backspace and tab) may ac-
tually enter a control character. If you have no convenient way of typing control characters, you
may change these parameters to ordinary printing characters.
To get back to Command Mode from Convers Mode, you must type a special character. The de-
fault character is a CTRL-C and it may be changed with the
COMmand
command. Typing the
COM-
mand
character when the unit is already in Command Mode does nothing. You may also return to
the Command Mode by sending a break signal over the data line to the unit. A break signal is not
an ASCII character but some keyboards provide a special key to accomplish this.
TRANSPARENT MODE
An application for which packet radio is very well suited is transfer of large amounts of data be-
tween Computers. For some types of data transfer operations, Convers Mode will work very well.
However, you may want to send special Information such as ready-to-run programs to another
Amateur. A .COM file on a CP/M System or even a BASIC program may contain many strange char-
acters which could be confused with the special reserved characters in Convers Mode. For this type
of application, you will want to use Transparent Mode. Transparent Mode is a data mode like
Convers Mode, except that in this mode there are no special characters. Everything you type (or
everything your computer sends to the KAM) is sent over the radio exactly as it appeared to the
KAM. Packets are sent at regular time intervals, or when a full packet of Information is ready. The
time intervals at which data i s packetized may be changed by the
PACTime
command.
The display characteristics of the KAM are also modified in Transparent Mode. Data is sent to
the terminal from the unit exactly as it is received over the radio channel, including all 8 bits of
each byte received. All features such as linefeed (LF) and (CR) insertion, (ESCAPE) translation, and
case conversion are disabled. In addition, echoing of input characters is disabled. None of the pa-
rameters which control these features in Convers Mode are changed by entering Transparent
Mode, and all display features are re-enabled when the unit i s returned to Command Mode. Most
of the informative messages which appear in Convers Mode, as the unit moves between discon-
nected and connected states, are also disabled.
In order to escape from Transparent Mode to Command Mode, you must follow a special proce-
dure. After a time interval equal to
PACTime
, the last data typed will have been packetized for
transmission (although it may not be transmitted yet). You must then wait an additional time,
which is set by the command
CMdtime
. Following this wait, you must type three CTRL-Cs (or what-
ever character is set by
COMmand
) within an interval
CMdtime
of each other. After a final
CMdtime
interval in which no characters are typed, you will see the cmd: prompt. If any characters are
typed in this interval (even if they are more Command characters}, the escape will be aborted and
the three Command characters will be sent as Packet data. You may also return to the Command
Mode by sending a break Signal over the data line to the unit. A break signal is not an ASCII char-
acter, but some keyboards provide a special key to accomplish this. If you set
CMdtime
or
PACTime
to zero, you will not be able to escape from Transparent Mode except by performing a hard reset
(power-down reset) or using the break signal.
PACKET TIMING FUNCTIONS
Four adjustable timing parameters are provided for configuring the KAM to your particular radio
environment, Some other parameters which are related to the timing parameters are discussed
here as well.
Amateur radio equipment varies greatly in the time delays required in switching from receive to
transmit and from transmit to receive. When two stations are sending packets back and forth,
these delays must be allowed for. If data is sent before the transmitter is operating, the packet will
not be transmitted properly. Similarly, if the receiving Station has not had sufficient time since it
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