PACKET
17
Hardware Flow Control
Hardware flow control monitors the voltages on the RTS and CTS pins of the RS-232 cable. There-
fore these two wired must be in the cable between your TNC and computer. The TNC holds CTS
high as long as it can receive data. Once its buffer gets full, it pulls this line low. The computer
program monitors this line and when it is pulled low, knows to stop sending data. When the line is
again pulled high by the TNC, the computer program will restart sending data. On the other hand,
the computer holds RTS high as long as it can receive data and pulls it low to tell the TNC to stop
sending data. The TNC always uses hardware flow control, so only wire the RTS and CTS pins if
your computer program is also using hardware flow control.
Convers Mode vs. Transparent Mode
In the Convers Mode there are many special characters. To list a few:
Command
Default
Description
SENDPAC
Ctrl-M
Causes a packet to be packetized
DELETE
Ctrl-H
Backspace character
REDISPLAY
Ctrl-R
Redisplays the keyboard buffer
CANLINE
Ctrl-X
Cancels a line
STOP
Ctrl-S
Stops output from TNC to computer
PASS
Ctrl-V
Pass a special character
These characters are all very useful when having a Packet conversation with someone. If you want
to send a packet, you hit the return. If you make a mistake, you can backup with the delete or
backspace key or kill the whole line with Ctrl-X. And if you really want to send one of this charac-
ters, you can always proceed it with the PASS character.
Transparent Mode is made for the sending of files, whether they be ASCII data files or program
files. The special characters do not mean anything to the TNC, they are just characters to be put in
a packet and sent to the radio. (XOFF, XON, STOP, START may be used depending on the settings
of XFLOW, TXFLOW and TRFLOW, see the flow control section.) A SENDPAC character will not
cause a packet to be packetized, instead this is controlled by a timer (PACTIME). This way short
lines do not make short packets, therefore less overhead and more efficient use of the frequency.
How congested the frequency is should be kept in mind when setting the PACLEN and MAXFRAME
parameters.
Besides ignoring special characters, Transparent Mode also ignores the settings of 8BITCONV and
PARITY. The TNC acts as though 8BITCONV is ON and PARITY is 4 (none), so be sure the com-
puters on both ends of the connection are set the same. All monitor commands are treated as OFF
in Transparent Mode. All you will see, is what is being sent to you. You would probably want to set
USERS to 1, so no one interferes with the transfer. The setting of ECHO is also ignored. Even if
ECHO is ON, Transparent Mode will not echo to the attached terminal. Some programs allow for lo-
cal echoing to the screen while uploading.