MFJ-1270C/1274C MANUAL ADVANCED OPERATION
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prompt. If any characters are typed during this interval (even Command Mode
entry characters) the escape will be aborted and all the Command Mode entry
characters that have been typed will be sent as packet data. If you set
CMDTIME
to zero you will not be able to escape from Transparent Mode using
this second procedure.
Flow Control
Whenever data is transferred to computers (home computers or TNCs), there is a
chance that the data will be received faster than the computer can handle it.
Some programs try to deal with this by providing data buffers for storing
incoming data until the program is ready for it. However, this merely postpones
the problem, since there is a limited amount of room in any buffer. In order to
prevent loss of data the computer must be able to make whatever is sending data
stop sending, and later tell it to resume sending. If you are a home computer
user, you are probably already familiar with one type of flow control, which
allows you to stop the output from the computer while you read it and restart it
when you are ready for more.
The MFJ TNC's input buffer may fill up in Command Mode if you try to type
too long a command. In Converse Mode the buffer may fill up for any of several
reasons: you may be using a faster serial port baud rate than the radio data rate;
radio data transmission may have slowed down because of noise or other users
on the channel; the person or computer at the other end may have stopped output
from that TNC. The MFJ TNC will signal the computer to stop sending data
when there is room remaining for about 80 characters in the buffer. When the
buffer fills up entirely, data will be lost. When the buffer empties so that there is
room for at least 270 characters, the MFJ TNC will signal the computer to start
sending data again.
A computer file transfer program may be unable to process data fast enough to
keep up with output from the MFJ TNC. In order to be sure of reading every
character, a computer must respond to interrupts from its I/O devices. Some
simple programs may poll the input register for new data. If the polling is not
done often enough, data may be lost. Some computers disable interrupts during
disk accesses. If the program enters a routine which will not allow it to check for
data or respond to it, it should signal the MFJ TNC to stop sending data.
There are two methods of providing flow control which are supported by the
MFJ TNC. XON/XOFF flow control, sometimes called "software flow control,"
is accomplished by sending a special character (usually <CTRL-S>) to request
