Radio Shack TRS-80 Model 100 Basic Manual page 172

A start bit is always used to signal the beginning of a new character to the receiving
device.
A parity bit is sometimes added to provide a means of error detection. If the parity is
specified as odd, the parity bit will equal zero if the sum of the data bits is odd, but
the parity bit will equal one if the sum of the data bits is even. Thus, with odd parity,
the sum of. the' data bits plus the parity bit is always odd. Similarly, with even parity,
the sum of the data plus parity bits is always even.
The stop bites) follow the parity bit, if any, and indicate the end of a character to the
receiving device. While different systems use various stop bit lengths, the Model 100
allows either one or two stop bits.
Before you can use the RS-232C serial port on the Model 100, you must set the
following parameters:
1. Baud rate, r: The baud rate is the speed at which the characters are sent. The
following values are permitted:
r
Baud rate
r
Baud rate
1
75
6
2400
2 110 7 4800
3 300 8 9600
4
600
9 19200
5
1200
Note: 300 and 1200 baud are common speeds for transmission of data over
telephone lines using audio tones. The Model 100 has a built-in modem which
allows a direct connection to the telephone lines for 300 baud communications.
However, if you use the serial port, rather than audio tones through the modem,
you can communicate with other serial devices at any
of
the baud rates listed
above.
2.
Word length, w: This is the number of data bits used to represent each ASCII
character. The three values permitted with the Model 100 are six, seven, or eight
data bits.
3.
Parity, p: The parity bit, if any, is specified as one of:
p Parity
E Even
o
Odd
N None
I Ignore
4. Number of stop bits, b: You can specify either one or two stop bits (s= I or
s=2).
5.
Line Status (XON/XOFF), s: Serial communications devices typically use some
form of "handshaking" to synchronize transmitting and receiving. This is
frequently necessary at the higher baud rates (1200 and above) to prevent
transmitting characters to a device which is not ready to receive them.
The Model 100 uses a handshaking technique known as XON/XOFF. The
receiving device sends an XOFF signal to the transmitting device if it cannot
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