Commodore VIC-20 Programmer's Reference Manual page 272

SENDING DATA TO AN RS-232 CHANNEL
When sending data, the output buffer can hold 256 characters
before a full buffer hold-off occurs. The system will wait in the
CHROUT routine until transmission is allowed or the RUN/STOP-
RESTORE keys are used to recover the system through a WARM
START.
BASIC SYNTAX
CMD If—acts same as in BASIC spec.
PRINT#lf,<varrable list>
KERNAL ENTRIES
CHKOUT (SFFC9)—See Section 3 for more information on entry
and exit conditions.
CHROUT (SFFD2)—See Section 3 for more information on entry
conditions.
NOTES
IMPORTANT: There is no carriage-return delay built into the output
channel so a normal RS-232 printer cannot correctly print, unless
some form of hold-off (asking the VIC to wait) or internal buffering is
implemented by the printer. The hold-off can easily be implemented
in your program. If a CTS (x-)ine) handshake is implemented, the
VIC buffer will fill and hold off more output until transmission is
allowed by the RS-232 device.
The routine CHKOUT handles the x-line handshake, which
follows the EIA standard (August 1979) for RS-232-C interfaces.
The RTS. and DCD lines are implemented with the VIC defined as
the Data Terminal Device.
CLOSING AN RS-232 DATA CHANNEL
Closing an RS-232 file discards all data in the buffers at the time
of execution (whether or not it had been transmitted or printed out),
stops all RS-232 transmitting antf receiving, sets the RTS and Sout
Sines high, and removes both RS-232 buffers.
BASIC SYNTAX
CLOSE If
256
I
I