Q33732: COM1 and COM2: Communications Device Default Buffer Size

Article: Q33732
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | docerr B_BasicCom | mspl13_basic
Last Modified: 11-JUN-1990

The receive and transmission buffer sizes for COM1 and COM2 default to
512 bytes in Microsoft QuickBASIC versions 4.00, 4.00b, and 4.50, and
in Microsoft BASIC Compiler versions 6.00 and 6.00b [and in Microsoft
BASIC Professional Development System (PDS) version 7.00, as described
in a separate article].

A sentence under the /C:buffersize option (in the section "Using BC
Command Options") on Page 210 of the manuals listed below incorrectly
states the following: "the default receive-buffer size is 256 bytes
total for both ports." The default receive-buffer size is actually 512
bytes for both the COM1 and COM2 communications ports. The affected
manuals are as follows:

1. Page 210 of "Microsoft QuickBASIC 4.0: Learning and Using
   QuickBASIC" for QuickBASIC 4.00 and 4.00b

2. Page 210 of "Microsoft BASIC Compiler 6.0: Learning and Using
   QuickBASIC" for Microsoft BASIC Compiler versions 6.00 and 6.00b

The section "Using BC Command Options" on Page 354 of the following
manual incorrectly states that "the transmission buffer is allocated
128 bytes for each communications port" and should be changed to say
that 512 bytes is the default transmission buffer size:

   Page 354 of "Microsoft BASIC 4.5: Programming in BASIC" manual for
   QuickBASIC version 4.50

Note that the default receive buffer size (512 bytes) is CORRECTLY
documented in the following places:

1. Page 298 in the "Microsoft QuickBASIC 4.0: BASIC Language
   Reference" manual for versions 4.00 and 4.00b

   This page correctly documents the RB[n] and TB[n] options for the
   OPEN COM statement. RB[n] changes the receive buffer size and TB[n]
   changes the transmission buffer size in the OPEN COM statement. The
   RB option overrides the receive buffer size specified by the /C
   option (if any). There is no compile-time option (including /C)
   that affects the transmission buffer size; TB is instead used in
   the OPEN COM statement at run time.

2. Page 151 of "Microsoft QuickBASIC 4.5: Learning to Use" manual for
   version 4.50

3. Page 354 of "Microsoft QuickBASIC 4.5: Programming in BASIC" manual
   for version 4.50

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.