Commodore Plus 4 - Page 393

The Modem and Other RS232 Devices 381
packaged with the device or interface for differences. The use of the RS232 port in
machine language is virtually identical to its use in BASIC. Machine-language
programmers will find both the BASIC and machine-language descriptions
helpful.
Using an RS232 Device with BASIC
The RS232 port is opened as an input/output file. When it is opened, the
communications protocol to be used is established through the control and
command registers. The values of these registers are passed to the RS232 port
through the file name parameter of the OPEN command. That is, the first two
characters of the parameter are interpreted as the CHR$ codes for the control and
command register values. Any subsequent characters are ignored. The secondary
address parameter of the OPEN command is ignored. The OPEN command
syntax is
OPEN fUenumber,&,0,ClIR$(control register)CHR$( Gonunand
register^)
where filenumber is the logical file number to associate with the RS232 port. The
logical file number can be 1-255 (128-255 causes a linefeed to follow each
carriage return). The control and command register values are passed as a
two-character string.
The control register values are as follows:
Bit(s)
0-3
Meaning
baud rate generator
0000 =
0001 =
0010 =
0011 =
0100 =
0101 =
0110 =
0111 =
1000 =
1001 =
1010 =
1011 =
1100 =
1101 =
1110 =
mi =
16 times external clock
50 baud
75
109.92
134.58
150
300
600*
1200*
1800*
2400*
3600*
4800 *
7200*
9600 *
19200 *