20
MT2834ZPX Owner's Manual
As a general rule, you should try to transmit files in already-
compressed form rather than relying on V.42bis hardware
compression. Because software compression is more efficient than
hardware compression, you will have a higher throughput with the
former. Of course, this efficiency does not include the time spent
compressing and decompressing .ZIP or .SIT files, but it will save on
phone bills. And hardware compression will still be there for those
occasions when it is inconvenient to compress a file with software.
Disabling Error Correction
By default, the MT2834ZPX is set to auto-reliable mode. In this mode
the MT2834ZPX determines during the handshake whether the other
modem is using V.42 error correction. If it is, the MT2834ZPX then
switches itself to reliable mode and enables error correction. If it is not,
the MT2834ZPX remains in non-error correction mode.
Typically, we recommend that you leave the MT2834ZPX set to auto-
reliable mode (&E1). However, you may encounter some
circumstances in which the MT2834ZPX will work better with error
correction turned off. For example, it has been reported that on
CompuServe error correction will slow file transfers at modem speeds
of 9600 bps and under. If this is a problem for you, you can turn off
error correction with the command AT &E0, or you can include the
command in your initialization string as follows:
AT &F S0=0 X4 &E0 ^M
The 16550 UART and Windows 3.1
Windows 3.1 may cause a loss of data when communicating at high
speed, even with a 16550 UART installed. Because Windows is
multitasking—it switches between several programs running at the
same time—it can make the serial port wait briefly while Windows
performs other tasks. Meanwhile, incoming data can be lost. The older
8250A and 16450 UARTs can store data in a one-byte first in-first out
(FIFO) buffer (a memory area in the UART in which the first bit in is
the first out), but once the buffer is full, the data is lost. The 16550 has
a 16-byte FIFO buffer, which accounts for much of its high speed.
However, in Windows 3.1, the 16550’s FIFO buffer is disabled by
default.