Asynchronous Transmission
In asynchronous DTE/DCE interface operation, character beginnings are marked
by start bits. The receiver samples the bits at fixed time intervals
after the leading edges of start bits. Characters end in stop bits.
The following depicts an ASCII pulse train for the characters BAT. The train
also depicts the start and stop bits for the RS-232 coded signals.
The use of parity bits is optional depending on the asynchronous character
format selected.
When sending and receiving data, the modem supports the following asynchronous
character formats:
Start Bits Data Bits Parity Stop Bits
1 7 even/odd 1 or more
1 7 none 2
1 7 mark/space 1 or more
1 8 none 1 or more
At speeds of 1200 bits/s or higher, the modem always generates data in a
10-bit format, including the start bit. In the modem command state, information
exchanged between the DTE and modem consists of commands and responses that
are not transmitted or received over the phone line. The character formats
supported by a particular modem are provided in your installation information
for the modem.
Click here to return to the Contents page.