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What does 8-N-1 mean?

"8-N-1" or "8-None-1" refers to the standard breakdown of data words in the serial format. It is what makes it possible for one modem to understand the stream of 1's and 0's sent by the other modem. With parallel data, the first bit is on the first wire, the second on the second wire, and so on, and it is much easier to keep track of data words. When data is lined up in series, the modem or computer has to know when one data word starts, when it stops, and when to expect the next. As a standard, a data word will consist of 10 or 11 bits. It starts with a "start bit" (obviously) followed by the data word, a "parity bit", and a stop bit.

The new ASCII standard allows for 255 encoded characters, 11111111 in binary, so it is necessary to have 8 bits to represent all of the ASCII characters. For this reason, the standard word size used in serial communication is 8 bits.

Parity is a simple way of checking to make sure all the data got sent correctly. "Even" parity means that a 1 is sent if there were an even number of data bits sent ahead of it, and "odd" parity means a 1 is sent for an odd number of data bits. The problem with this is that if two data bits were lost (not just one) the parity won't help at all. With today's error-correcting modems, parity is unnecessary.

8-None-1 means that data will start with a start bit, include 8 true data bits, no parity, and 1 stop bit (10 bits in all).


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