Microsoft KB Archive/45486

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Knowledge Base

Can't Use Printer Port for Serial COM Input in QuickBASIC

Article ID: 45486

Article Last Modified on 8/16/2005


  • Microsoft QuickBasic Compiler for Macintosh 1.0
  • Microsoft BASIC Compiler 6.0b
  • Microsoft BASIC Interpreter 2.0
  • Microsoft BASIC Interpreter 2.1 for Macintosh
  • Microsoft BASIC Interpreter 3.0 for Macintosh

This article was previously published under Q45486


There are two RS-232 serial communications ports on each Apple Macintosh system that are normally configured as one COM port and one printer port.

Microsoft QuickBASIC Version 1.00 for the Apple Macintosh uses only one port as the COM port and one as the printer port. Although these two ports are physically and logically identical, QuickBASIC recognizes only the first one as the COM port (telephone icon) and the second as the printer port (printer icon).

You can use only the OPEN "COM1:baud,parity,data,stop" statement to set the communications parameters (for input, output, and random access) on the telephone icon port. On the printer port, marked with the printer icon, QuickBASIC cannot change the baud rate, parity, data bits, or stop bits. This limits input possibilities.

This information also applies to the Microsoft BASIC Compiler 1.00 for the Macintosh and the Microsoft BASIC Interpreter Versions 2.00, 2.10, and 3.00 for the Macintosh.


When the AppleTalk Network cable is connected to the printer port (normal configuration), then the LLIST and LPRINT statements in QuickBASIC send output to the COM port (to a directly connected Apple ImageWriter printer only); and the "LPT1:" and "LPT1:PROMPT" device names send output to the AppleTalk Network printer that is currently selected in the Chooser (in the Apple menu).

Additional query words: BasicCom MQuickB

Keywords: KB45486