Q43401: How to Test for an Error When Using _bios_serialcom Service

Article: Q43401
Product(s): See article
Version(s): 5.00 5.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | s_quickc docerr | mspl13_c
Last Modified: 14-APR-1989

Problem:

I am using the _COM_RECEIVE function of _bios_serialcom to read data
from a communications port. How do I determine if an error has
occurred?

Response:

Referring to the table on Page 144, Page 145 of the "Microsoft
Optimizing C Run-Time Library Reference" and the "Microsoft QuickC
Run-Time Library Reference" states the following:

   If an error occurs, at least one of the high-order bits will be
   set.

While this is correct, it is misleading. It is true that at least one
of the high-order bits will be set if an error occurs. However, it is
not true that if ANY high-order bit is set, an error has occurred. An
error has occurred if, and only if, any of the following four bits are
set:

   Bit     Meaning if Set

   15      Timed out
   11      Framing error
   10      Parity error
    9      Overrun error

The sentence quoted above would be more accurate if it read as
follows:

   If an error occurs, any of bits 9, 10, 11, or 15 will be set.

This information is explained on Page 431 of "Advanced MS-DOS" by
Ray Duncan.

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