Commodore Plus 4 - Page 218

SECTION 13 Introduction
RS-232
Interface
Opening
The
RS-232
Channel
Your Commodore Plus/4 has a built in RS-232 interface for connection
to any RS232 modem, printer, or other device. To connect a device to
your Plus/4 requires a cable and some additional programming. The
Commodore modem connects directly.
RS-232 on the Plus/4 is standard RS-232 format, bat the voltages are
TTL levels (0 to 5V) rather than the normal RS-232 -12 to 12 volt range.
The cable between the Commodore Plus/4 and the RS-232 device —
should accommodate the necessary voltage conversions. (The Com
modore RS-232 interface cartridge handles this properly.)
The RS-232 interface software can be accessed from BASIC or from
the KERNAL for machine language programming. This section ad- —
dresses the use of RS-232 from BASIC. For more detailed information,
and for use from machine language, consult the Commodore Pius<'4
Programmers Reference Guide. RS-232 from BASIC level uses the
normal BASIC commands: OPEN, CLOSE, CMD, INPUT#. GET#,
PRINT#, and the reserved variable ST. INPUT# and GET# recall
data from the receiving buffer, while PRINT# and CMD place data into
the transmitter.
Only one RS-232 channel should be open at any time; a second OPEN
statement causes the receive buffer pointer to be reset, causing any —
characters in the buffer to be lost.
Up to 4 characters may be sent in the filename field. The first two are
control and command register characters; the other two are reserved
for future system options. Baud rate, parity, and other options can be —
selected through this feature.
Basic Syntax: —
OPEN if. 2,0,<" >control register command register<">
EXAMPLE:
OPEN 2,2,0, CHR$(5)+ CHR$(15) —
/f—Normal logical file id. (1 -255). If If > 127, then linefeed follows
carriage return.
control register—Single byte character (see Figure 1) (required to
specify baud rate)
command register—Single byte character (see Figure 2)
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