halco@iccgcc.decnet.ab.com (10/13/90)
With Hayes-type modems, it's common to have the modem report the data rate for the computer after completing the connection with a message like "CONNECT 1200", or whatever the data rate should be. My question is, is this pretty universal, or is there some more bullet-proof way for communication software to determine what rate to use when answering a call? The method should not rely on the originating software, but can be restricted to the IBM-PC compatible world. Any and all responses will be appreciated.
lstowell@pyrnova.pyramid.com (Lon Stowell) (10/17/90)
Answer--Autobaud procedures. Typically the dialer hits the CR key repeatedly until the prompt appears correctly. The Diallee starts the baud rate at a default value and examines the received character along with parity error, false start, and framing error status bits from the hardware. By these and a simple look-up table, the correct baud rate can be determined. If the range is fairly simple...say 2400-9600, it is possible to determine parity and bits/character as well. Over wider ranges it gets pretty tricky.