Commodore Plus 4 - Page 384

372 Using Peripheral Devices
chapter. Commercial software may or may not be able to access an RS232
printer. When selecting a printer, make sure that the software you intend to use
will access it properly.
Each type of printer accepts a different set of commands. Some may allow the
printing of graphics characters, upper and lower case, custom designed charac
ters, and so on. It is not possible to completely describe all of the commands
accepted by every type of printer here. Refer to the manual that comes with your
printer for the commands it accepts.
This section describes the method of accessing any printer through the serial
port and, for exemplary purposes, describes the commands accepted by Commo
dore's MPS-801 printer.
Using a Printer with BASIC
The first step in accessing the printer is to issue an OPEN statement:
OPEN filenumber,devloe,seoondary address
The filenumber is the logical file number to be associated with the printer. It can
be 0-255, but 128-255 causes a linefeed character to be sent after the carriage
return at the end of a line. The MPS-801 does a carriage return and linefeed upon
receiving a carriage return character or a linefeed character. As a result, a logical
file number from 128 to 255 causes a blank line after each printed line. Other
printers may react differently to the two types of logical file numbers. The device
is the device number; it is generally 4 for a printer. The MPS-801 can be switched
between 4 and 5. The secondary address is interpreted by the printer.
Printers generally accept commands at two levels. The first is within the
secondary address sent to the printer in the open statement. The second is special
nonprinting control characters that the printer interprets. The MPS-801 accepts
only two values for the secondary address:
0 = default setting is upper case/graphics mode.
7 = default setting is upper/lower case mode.
Other printers may accept different secondary addresses with different results.
Once the printer file is open, data may be directed to the printer in two ways.
The first is the CMD command. This is particularly useful in direct mode to get a
printout of the program currently in memory. The CMD command changes the
default output device to the file named:
CMD filenumber