Q12027: "Bad File Name"; OPEN "COM1:"; 8 Data Bits Must Have No Parity

Article: Q12027
Product(s): See article
Version(s): 1.00 1.01 1.02 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 4-SEP-1990

When you use the OPEN "COM" statement with the data bits set to 8 and
parity set to Even or Odd, you will get a "Bad File Name" error. For
example, "Bad File Name" occurs at run time when you open the serial
communications port as follows:

   OPEN "COM1:9600,E,8,1" AS 2

This error disappears using 7 data bits, or No (N) parity.

When you specify 8 data bits, you must specify a parity of N. This is
a limitation in the design of QuickBASIC versions 1.00, 1.01, 1.02,
2.00, 2.01, 3.00, 4.00, 4.00b, and 4.50; Microsoft BASIC Compiler
versions 6.00 and 6.00b for MS-DOS and MS OS/2; and Microsoft BASIC
PDS versions 7.00 and 7.10 for MS-DOS and MS OS/2.

As a workaround in QuickBASIC versions 4.00 and later, Microsoft BASIC
Compiler versions 6.00 or 6.00b, or BASIC PDS, you can call a
Microsoft C version 5.10 routine from BASIC to do the communications
with 8 bits and odd or even parity. The following book will help in
doing this:

   "Microsoft C Programming for the IBM" by Robert Lafore (published by
   the Waite Group)

The QuickBASIC Compiler, BASIC compiler 6.00, and BASIC PDS 7.00 are
designed with a 10-bit data frame for communications. The frame is as
follows:

            1 2  -  8 9 A
            S DDDDDDD P S

Bit  1     = Start Bit    (Always 1)
Bits 2 - 8 = Data Bits    (7 or 8)
Bit  9     = Parity       (Odd, Even, or None)
Bit  A     = Stop Bit(s)  (1 or 2)

The combination of the bits should add up to 10 bits. When you try to
set 1 start + 8 data + 1 parity + 1 stop, that adds up to an 11-bit
data frame, which BASIC is not designed for.

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