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Q37347: "Device Unavailable" on OPEN "COM1:" Compiled with BC /O/S

Article: Q37347
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom buglist4.00 buglist4.00b buglist4.50 | mspl13_basic
Last Modified: 12-JAN-1990

A program that accesses the serial communications ports with OPEN
"COM1:" or "COM2:" produces a "Device Unavailable" (run-time error 68)
message if it is compiled using BC.EXE with the /O (stand-alone .EXE)
and /S (minimize string space) options together.

To work around this limitation, do not use the /S and /O options
together when compiling programs that access the communications ports.

Microsoft has confirmed this to be a problem in Microsoft QuickBASIC
4.00, 4.00b, and 4.50 for MS-DOS and in Microsoft BASIC Compiler 6.00
and 6.00b (buglist6.00 buglist6.00b) for MS-DOS and MS OS/2. We are
researching this problem and will post new information here as it
becomes available. This problem does not occur in Microsoft BASIC PDS
Version 7.00 for MS-DOS and MS OS/2 (fixlist7.00).

The sample program below runs properly inside the environment;
however, when compiled to an .EXE file using the BC /O and /S options,
a "Device Unavailable" error message is produced on the OPEN "COM1:"
statement. [The problem can also occur when you use the ON COM(n)
GOSUB statement.]

The following is a code example:

OPEN "COM1:9600,N,8,1,CS,DS" FOR RANDOM AS 1
CLOSE 1

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