Very Computer

The most common cause of comm lockups in Windows is a 16550-compatible chip
that isn't fully compatible. Typically this is seen on Pentium systems with
serial ports integrated on the motherboard, but it can also happen with
add-on cards, particularly "multi-I/O" cards based on popular SMC chips.
(See "PC Hangs While Running a Communications Application" at
http://www.microsoft.com/Support/KBSL/DEVELOPR/win_dk/Q119853.htm)

* If you are running Windows for Workgroups 3.11, one fix is to download and
install the updated SERIAL.386 driver that implements a workaround for this
problem. But see warning below. (This fix wont work for standard Windows
3.1 or 3.11.)

* You should be able to completely solve the problem by turning off the UART
buffers. To do that, put the following in the [386Enh] section of your
SYSTEM.INI file:
COMnFIFO=0
where n is the number of your modem COM port (e.g., COM2FIFO=0). The
drawback is that you then won't get the benefit of the 16550 FIFO buffers.
(See "Do I need a 16550 UART? What is a UART?") For that you will need to
upgrade to Windows for Workgroups and apply the SERIAL.386 fix (see above),
or get a replacement UART.

WARNING: Although Microsoft specifically identifies the SMC 665 "multi-I/O"
chip as the problem, the author has personally verified that the problem
also exists in the SMC 666 "multi-I/O" chip (FDC37C666GT). Furthermore,
although the problem is reportedly fixed in current chip production, the
author has personally verified that the problem still exists in multiple
brands of I/O cards on the market as of August 1995. Worse, the author has
also personally verified that Microsofts updated SERIAL.386 is not fully
satisfactory: lockups are very rare but not entirely eliminated, and Windows
multitasking is adversely affected during certain communications operations.
(Negotiating a dialup PPP link with Trumpet Winsock 2.1F seems to trigger
the problem.) The only fully effective workaround is to disable the FIFO
buffers (as described above). FOR THIS REASON THE AUTHOR DOES NOT RECOMMEND
PRODUCTS THAT USE SMC "MULTI-I/O" CHIPS.

REQUEST: The author is looking for multi-I/O cards with real 16550 UARTs to
recommend as replacements for SMC-based multi-I/O cards. Any help would be
appreciated.

--
Best regards,

28800 Modem FAQ: http://web.aimnet.com/~jnavas/modem/faq.html

The most common cause of comm lockups in Windows is a 16550-compatible chip
that isn't fully compatible. Typically this is seen on Pentium systems with
serial ports integrated on the motherboard, but it can also happen with
add-on cards, particularly "multi-I/O" cards based on popular SMC chips.
(See "PC Hangs While Running a Communications Application" at
http://www.microsoft.com/Support/KBSL/DEVELOPR/win_dk/Q119853.htm)

* If you are running Windows for Workgroups 3.11, one fix is to download and
install the updated SERIAL.386 driver that implements a workaround for this
problem. But see warning below. (This fix wont work for standard Windows
3.1 or 3.11.)

* You should be able to completely solve the problem by turning off the UART
buffers. To do that, put the following in the [386Enh] section of your
SYSTEM.INI file:
COMnFIFO=0
where n is the number of your modem COM port (e.g., COM2FIFO=0). The
drawback is that you then won't get the benefit of the 16550 FIFO buffers.
(See "Do I need a 16550 UART? What is a UART?") For that you will need to
upgrade to Windows for Workgroups and apply the SERIAL.386 fix (see above),
or get a replacement UART.

WARNING: Although Microsoft specifically identifies the SMC 665 "multi-I/O"
chip as the problem, the author has personally verified that the problem
also exists in the SMC 666 "multi-I/O" chip (FDC37C666GT). Furthermore,
although the problem is reportedly fixed in current chip production, the
author has personally verified that the problem still exists in multiple
brands of I/O cards on the market as of August 1995. Worse, the author has
also personally verified that Microsofts updated SERIAL.386 is not fully
satisfactory: lockups are very rare but not entirely eliminated, and Windows
multitasking is adversely affected during certain communications operations.
(Negotiating a dialup PPP link with Trumpet Winsock 2.1F seems to trigger
the problem.) The only fully effective workaround is to disable the FIFO
buffers (as described above). FOR THIS REASON THE AUTHOR DOES NOT RECOMMEND
PRODUCTS THAT USE SMC "MULTI-I/O" CHIPS.

--
Best regards,

28800 Modem FAQ: http://web.aimnet.com/~jnavas/modem/faq.html

A common cause of this problem is a 16550-compatible chip that isn't
fully compatible. Typically this is seen on Pentium systems with serial
ports integrated on the motherboard, but it can also happen with add-on
cards, particularly "multi-I/O" cards based on popular SMC chips.
<http://www.microsoft.com/Support/KBSL/DEVELOPR/win_dk/Q119853.htm>

   * Updated drivers are available from SMC and Microsoft to work around
     the problem. The SMC package
     <ftp://ftp.smc.com/pub/chips/superio/serial.zip> includes both SMC's
     updated COMM.DRV for regular Windows 3.1 and Microsoft's updated
     SERIAL.386 for Windows for Workgroups 3.11; the Microsoft package
     <ftp://ftp.microsoft.com/Softlib/MSLFILES/WG1001.EXE> includes only
     Microsoft's updated SERIAL.386 (10,620 bytes dated 2/17/94). But see
     warning below.
   * Alternatively you should be able to completely solve (or simply test)
     the problem by turning off the UART buffers. To do that, put the
     following in the [386Enh] section of your SYSTEM.INI file:
     COMnFIFO=0
     where n is the number of your modem COM port (e.g., COM2FIFO=0). The
     drawback is that you then won't get the benefit of the 16550 FIFO
     buffers.

Warning: Although Microsoft specifically identifies the SMC '665 chip as
the problem, the author has personally verified that a problem also exists
in the SMC '666 chip (FDC37C666GT). Furthermore, although the original FIFO
problem is reportedly fixed in current chip production, the author has
personally verified that a problem (perhaps a different problem) still
exists as of August 1995. The author has also personally verified that:

   * SMC's updated COMM.DRV does not correct this current problem; and
   * Microsoft's updated SERIAL.386 is not fully satisfactory: lockups are
     very rare but not entirely eliminated, and Windows multitasking is
     adversely affected during certain communications operations (e.g.,
     negotiating a dialup PPP link with Trumpet Winsock 2.1F).

The only fully effective workaround is to disable the FIFO buffers (as
described above). For this reason the author does not currently recommend
products that use SMC "multi-I/O" chips.

--
Best regards,

       28800 Modem FAQ: http://web.aimnet.com/~jnavas/modem/faq.html