3860/80 User’s Manual
12-2
Parameters
In order for devices to communicate via RS-232, the character frames (baud rate, number of
data bits, parity, number of stop bits), as well as the handshaking, must be set the same at the
transmitter and receiver.
The factory default settings for the character frame are 9600 baud, 1 start bit, eight data bits,
one stop bit. The factory defaults for parity are: Ignore received parity and transmit even
parity.
The computer expects to receive the READY/BUSY status (handshaking) and fault status
from the printer by receiving a special character (busy by code), or by reading the DC voltage
on one or more of several signal wires (busy by level).
As shipped, the printer is set to indicate READY/ BUSY by code (XON/ XOFF) and also by
level (DTR and SRTS). A fault condition is reflected in XON/XOFF and DTR.
DOS Machines
For those using personal computers, the default handshaking is compatible, and the default
character frame matches the DOS defaults. Always set DOS
serial
parameters explicitly with
the MODE command in DOS.
Seven or Eight Data Bits
A few years ago, a typical character-imaging device (CRT terminal or printer) would render
about 94 symbols. This reflects the limits of the teletype machine, which is a conceptual
descendent of the typewriter. It only takes seven bits of data to select among 128 symbols or
control codes.
When seven-bit data is used, the eighth bit in the byte is often used as a parity bit. The parity
bit might be set so that the number of ones in the byte is always even (even parity) or always
odd (odd parity). This serves as an error check. The parity bit can also be set to always be
zero (space) or always be one (mark).
As character-imaging devices have come to support more symbols, such as line-drawing
symbols, and characters from non-English alphabets, a common method for transmitting these
additional characters is to use the eighth bit for data.
