One State. Zero State receiving end of the circuit also makes the same calculation, it can be used to indicate if an error has occurred. This is called odd, or even, parity transmission and is useful when transmitting blocks of data that are not seen on the screen.

More often than not, the first-time modem user gets garbage on the CRT screen. Usually, the response is, "This blankey-blank| "#$%&'( )*= (fill in computer, software, modem, telephone line, host, or other favorite culprit).

Actually, the culprit is probably the operator's unfamiliarity with the usage of the eighth bit for parity error checking. Keep in mind that if the software accepts the eighth bit, and it is present, your computer is switched into the upper 128 characters which represent graphics. If the garbage consists of a lot of graphics symbols, the computer you are tied to may want a 7-bit, rather than an 8-bit byte.

As a starting point, go to the communication parameter section of your software. Select a 7-bit byte (sometimes called a "word," even though it is only one letter in length), no parity and one stop bit. This setup will usually suffice for most systems. If you still get "garbage," contact the system operator (SYSOP) and determine what byte construction the system requires.

I had hoped to put the theory section behind us this time, but there is so much to tell you that we'll continue in the next installment. ■

Figure 2

One State

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