AT&T 6300 Programmer's Manual page 152

Asynchronous Communications
200-280 This section performs Full Duplex
110
between
the Video Screen and the device connected to
the RS232 connector as follows:
• Read a character from the keyboard into A$.
Note that INKEY$ returns a null string if no
character is waiting.
• If no character is waiting then check to see if
any characters are being received. If a character
is waiting at the keyboard then:
• If the character was the MENU Key, then the
user is ready to download a file, so retrieve the
file name.
• If character (A$) is not the MENU key then
send it by writing to the communication file
(PRINT #1 ... ).
• At 230, check if any characters are waiting in
COM buffer. If not, then go back and check
keyboard.
• At 240, if more than 128 characters are waiting,
then set the PAUSE flag, thereby suspending
input andsend XOFF to the host, thus
stopping further transmission.
• At 253-257, strip out linefeed characters before
sending buffer contents to the screen. Otherwise
the PC executes a LF with each CR, resulting in
double spacing.
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