Multi Tech MT5656ZDX modem

Command: $SBn Serial Port Baud Rate Note: Use this command with MT5600BA and MT5600BR only. Not supported by the MT5656ZDX/MT5656ZDXV

I read the fine manual (RTFM)

AT&V Lists Current Operating Parameters

.... regards Tony

Thanks Tony. This looks like the wrong device.

Hul

Anth> Command: $SBn Serial Port Baud Rate

Google found this:

Page 15: Command: $SBn Serial Port Baud Rate Note: Use this command with MT5600BA and MT5600BR only. Not supported by the MT5656ZDX/MT5656ZDXV

Page 36: Command: +VPR Select DTE/Modem Interface Rate (Turn Off Autobaud) Description: This command selects the DTE/modem interface rate. Syntax: +VPR=

Your Welcome.

Thanks Hamilton. I suspected something like the command you found, but didn't see anything likely.

Hul

Hamilton - no luck, that's the modem rate rather than the rs232 rate. Said differently, the data rate between the computer and the external modem is only 2400 baud and, apparantly, can't be changed. The VPR command alters the data rate between the external modem and whatever's on the other end of the telephone line. Thanks for looking, though.

Hul

Quite a lot of modems will automatically set their serial port bit rate to match what the host computer is doing. (That was part of the original purpose of the 'AT' command prefix - it gave the modem a couple of bytes to sync up to.) Just change the bit rate on the computer to whatever you want and the modem should change itself to match.

If you want to "lock" the speed in the modem for some reason, there is usually an AT command to do it, but I don't think it's standard - check the manual for your modem.

Also note that if the modem does data compression, it's pretty common to set the serial port bit rate on the computer to 2x - 4x the phone line speed, to let the compression work. The modem uses the flow control lines on the serial port to stop and start the data from the computer, so the modem only ends up with as much data as it can handle at the moment. Some modems with phone line speed of 9600 bps did compression, and I think all modems with phone line speeds of 14400 bps and up do compression. Just multiply the phone line speed by 2 or 4 and then round up to the next "standard" bit rate.

Matt Roberds

Are you sure that the modem does not support autobauding ?

Set the serial port to some higher speed, such as 115200 bit/s, then turn on the modem and send some characters or for instance the ATS0? command. Many modems autobaud with the "AT" characters.

Please note that when using simple FSK/PSK protocols without ECC or framing, the serial speed _must_ be the same as the line speed, so that 2400 bit/s makes sense for simple PSK.

In order to use different serial and line speeds, you need to configure the modem to some error correction mode. On the line, blocks of data are transferred usually as synchronous frames, handling error correction (or resends), data compression as well as flow control between modems.

With these assumption, the serial line speed can be higher (and should be, if compression is used) as the line speed.

Figure out what error correction modes are supported, select one of them, save settings and then try autobauding the serial line.

I think I had one of those back in the day, and I'm pretty sure it does. Been a long time though, I might not have the model number exactly the same. Many of them use the Rockwell V92 chipset, so lots of models are very similar in functionality.

Theo

Typically, any rate other 2400 showed a partial response or none at all. At 2400, "AT" returned OK, at 9600, if memory serves, just K and 38400 showed nothing. It does smell like an "autobaud" of some sort that requires info about it's operation but none is shown. The "user's guide" mentions a cdrom which wasn't included; maybe information was originally placed there. Overall, Multi Tech appears to be producing a "windows only" piece of gear and the mentioned cdrom may have contained installation software.

Hul

and 38400

Most modems today do serial line autobaud. Moreover, if allowed to, will default to 56k. See also TIA-678.

?-)