Multi-Tech Systems MT2834ZPX Disabling Error Correction, Uart and Windows, AT &F S0=0 X4 &E0 M

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.

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